U.S. Environmental Protection Agency Industrial Environmental Research PDA PHO/T 7fi
Office of Research and Development Laboratory
Cincinnati. Ohio 45268 December 1976
ENVIRONMENTAL
CONSIDERATIONS OF
SELECTED ENERGY
CONSERVING MANUFACTURING
PROCESS OPTIONS:
Vol. VIII. Alumina/
Aluminum Industry Report
Interagency
Energy-Environment
Research and Development
Program Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S.
Environmental Protection Agency, have been grouped into seven series.
These seven broad categories were established to facilitate further
development and application of environmental technology. Elimination
of traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields. The seven series
are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from
the effort funded under the 17-agency Federal Energy/Environment
Research and Development Program. These studies relate to EPA's
mission to protect the public health and welfare from adverse effects
of pollutants associated with energy systems. The goal of the Program
is to assure the rapid development of domestic energy supplies in an
environmentally—compatible manner by providing the necessary
environmental data and control technology. Investigations include
analyses of the transport of energy-related pollutants and their health
and ecological effects; assessments of, and development of, control
technologies for energy systems; and integrated assessments of a wide
range of energy-related environmental issues.
This document is available to the public through the National Technical
Information Service, Springfield, Virginia 22161.
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EPA-600/7-76-034h
December 1976
ENVIRONMENTAL CONSIDERATIONS OF SELECTED
ENERGY CONSERVING MANUFACTURING PROCESS OPTIONS
Volume VIII
ALUMINA/ALUMINUM INDUSTRY REPORT
EPA Contract No. 68-03-2198
Project Officer
Herbert S. Skovronek
Industrial Pollution Control Division
Industrial Environmental Research Laboratory - Cincinnati
Edison, New Jersey 08817
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE qF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
For sale by the Superintendent of Documents. UlS. Government Printing Office, Washington, D.C
.20*02
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DISCLAIMER
This report has been reviewed by the Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved -for publica-
tion. Approval does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
11
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FOREWORD
When energy and material resources are extracted, processed, converted,
and used, the related pollutional impacts on our environment and even on our
health often require that new and increasingly more efficient pollution con-
trol methods be used. The Industrial Environmental Research Laboratory
Cincinnati (lERL-Ci) assists in developing and demonstrating new and im-
proved methodologies that will meet these needs both efficiently and
economically.
This study, consisting of 15 reports, identifies promising industrial
processes and practices in 13 energy-intensive industries which, if imple-
mented over the coming 10 to 15 years, could result in more effective uti-
lization of energy resources. The study was carried out to assess the po-
tential environmental/energy impacts of such changes and the adequacy of
existing control technology in order to identify potential conflicts with
environmental regulations and to alert the Agency to areas where its activi-
ties and policies could influence the future choice of alternatives. The
results will be used by the EPA's Office of Research and Development to de-
fine those areas where existing pollution control technology suffices, where
current and anticipated programs adequately address the areas identified by
the contractor, and where selected program reorientation seems necessary.
Specific data will also be of considerable value to individual researchers
as industry background and in decision-making concerning project selection
and direction. The Power Technology and Conservation Branch of the Energy
Systems-Environmental Control Division should be contacted for additional
information on the program.
David G. Stephan
Director
Industrial Environmental Research Laboratory
i Cincinnati
iii
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EXECUTIVE SUMMARY
The aluminum industry is comprised of two basic operations: (1) the pro-
duction of alumina (A^C^) from bauxite by the Bayer process, and (2) the
reduction of alumina to aluminum metal by the Hall-Heroult electrolytic reduc-
tion process. These two operations are conducted at entirely separate locations.
Alternatives to the Bayer process examined in this study were hydrochloric
acid leaching, nitric acid leaching, and high temperature chlorination (To'th
process) of clays. The Alcoa chloride process and the use of titanium diboride
cathodes were examined as potential future alternatives to the conventional
Hall-Heroult process for aluminum production. In addition, the combination of
clay chlorination and the Alcoa process was compared with the conventional
Bayer-Hall technology.
Alumina
There are nine alumina plants within the U.S., six on the Gulf Coast, two
in Arkansas, and one in the Virgin Islands with a total capacity of 7,700,000
short ton/yr. The only domestic source of bauxite, the major raw material in
the production of alumina, is in Arkansas. The U.S. industry has always depended
largely on imports from the Carribean, northern South America, and Australia
for most of its supply of bauxite and alumina. Recent high levies on the baux-
ite exports and organized pressure to carry out the alumina production in these
countries make it unlikely that new Bayer alumina plants will be built in the
United States. However, if a successful clay-based process is developed, new
alumina plants may be built in the United States based on domestic alumina-
bearing kaolin and anorthosite clays, giving the United States some raw
material independence.
It is clear that more solid waste will be produced from treating clays to
recover alumina by any of the new processes—namely, nitric acid leaching,
hydrochloric acid leaching or clay chlorination—than is produced by the exist-
ing Bayer alumina process. However, with the processing plant near the mines,
the clay process wastes can be returned to mined-out areas.
In the case of the nitric acid and hydrochloric acid leaching processes,
the tail gases from the decomposition-acid recovery operation could contain
oxides of nitrogen and hydrogen chloride. Both couLd be removed by caustic
scrubbing,, but would result in water soluble nitrates and chlorides. The liquid*
waste from the nitric acid process will contain soluble nitrates. The hydro-
chloric acid and Toth chlorination processes will produce wastes containing
soluble chlorides, which are generally less objectionable than soluble nitrates
when discharged to the water environment.
IV
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Airborne emissions from the existing Bayer alumina plants are minor,
limited largely to 862 emissions from the boiler house, depending on the fuel
used, and dust from alumina and lime calcination. All can be controlled to
meet existing regulations. Nevertheless, pollution control costs would be
greater for any of the clay-based processes than those of the present Bayer
process, but not prohibitively high considering the value of the product. In
fact, the major environmental cost in nitric acid leaching is for sulfur dioxide
control, since coal is used as a fuel source. In costing the hydrochloric
acid leaching process low-sulfur fuel oil has been used as a fuel.
In comparing total energy use, the nitric acid leaching and clay chlorina-
tion processes appear to use about the same amount of energy, while hydrochloric
acid leaching uses about 30% more energy per ton of alumina. In addition, hydro-
chloric acid leaching appears to entail the highest operating costs while nitric
acid leaching costs compare favorably with those of a new Bayer plant. The
lowest estimated operating costs are found in clay chlorination. Since energy
use for clay chlorination is comparable to nitric acid leaching energy use,
future work on clay chlorination bears watching to prove out the energy use and
economics assumed here.
Aluminum
There are thirty-one aluminum smelters within the U.S., located along the
Mississippi and Ohio Rivers; in Massena, New York; and in Washington, Oregon,
and Western Montana. Total U.S. capacity is estimated at 5.0 million short
ton/yr. World consumption of aluminum has historically experienced a long-term
growth rate on the order of 10%/year. In the 1960's U.S. consumption grew by
an average 8%/year, but the trend among U.S. producers has been to lose market
share to foreign sources and to locate a larger amount of their smelter capacity
outside the United States; 15% is now located abroad.
Until recently, there has been little incentive in the United States to
reduce power consumption in aluminum smelters, which have traditionally been
located in low-cost electric power areas, in many cases a considerable dis-
tance from their markets. Much of this power is hydroelectric; but with limited
hydroelectric resources to be developed in the United States, this energy
source is not expected to play a major role in the expansion of the U.S. alumi-
num industry.
The use of titanium diboride cathodes would not significantly change the
nature of the liquid waste problem from the present operation. The new Alcoa
chloride process would introduce a new source of liquid and solid waste arising
as a consequence of bleeding the recirculating electrolyte. This waste would
consist of oxide sludges and sodium chloride.
It seems likely that the Alcoa chloride process and the use of the titanium
diboride cathodes in the existing Hall process will reduce air pollution from
cells and from the anode-making and -baking operations. In the case of the
Alcoa chloride process, the anodes will be inert and permanent, which means
that air pollution from anode-making would be completely eliminated from the
aluminum plant. In the case of the use of titanium diboride cathodes, the
v
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fluoride emissions per ton of aluminum produced would probably remain the same,
but the gas volume to be scrubbed would be lower. Moreover, we would expect
less carbon monoxide emissions per ton of aluminum produced.
Air pollution control costs for the cells and cell rooms of the new Alcoa
process and for use of titanium diboride cathodes in Hall cells appear to be
less than the costs for the existing Hall process. The Alcoa process would be
completely enclosed in order to recover chlorine for reuse and, while there
might be some losses of chlorine to the atmosphere, controlling chlorine emis-
sions to required levels should not be as difficult as for fluoride emissions.
However, the Alcoa process would add a new source of gaseous emissions, namely,
sulfur from the coking step and hydrogen chloride from the chlorinator tail
gas. Of course, both emissions can be controlled as required.
The Alcoa chloride process offers a potential route to making aluminum
that has energy savings of about 10% while keeping operating costs the same
or slightly lower than a plant based on Hall cell technology. The combination
of a clay chlorination process with the Alcoa process shows significant poten-
tial cost savings. The estimated cost of complete environmental control of
aluminum plants is a significant factor in both the capital and operating costs
of aluminum smelters, amounting to about 9% of the investment and 4% of aluminum
production costs in new Hall plants. We believe that the costs of achieving
environmental standards should be reviewed and that the possibilities for im-
proving the capital and operating costs of the pollution control system used in
Hall cells should be investigated. We also suggest that materials research be
undertaken on the subject of titanium diboride cathodes suitable in quality to
permit long operating life in the Hall cell environment. This development
would have a dramatic effect on energy savings in the aluminum industry. With
minimal capital charge requirement, such a development can be retrofitted to
existing aluminum plants. Other things remaining equal, there would be a
favorable environmental effect in reducing the emissions from the power plants
producing electricity for the smelters.
This report was submitted in partial fulfillment of contract 68-03-2198
by Arthur D. Little, Inc. under sponsorship of the U.S. Environmental Protection
Agency. This report covers a period from June 9, 1975 .to December 1, 1975.
vi
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TABLE OF CONTENTS
FOREWORD iii
EXECUTIVE SUMMARY iv
List of Figures ix
List of Tables x
Acknowledgments. xii
English-Metric (SI) Conversion Factors xiv
I. INTRODUCTION 1
A. BACKGROUND 1
B. CRITERIA FOR INDUSTRY SELECTION 1
C. CRITERIA FOR PROCESS SELECTION 2
D. SELECTION OF ALUMINA/ALUMINUM INDUSTRY PROCESS OPTIONS 4
II. FINDINGS AND CONCLUSIONS 7
A. PROCESS CHANGES IN PRODUCTION OF ALUMINA 7
1. Solid Waste 7
2. Liquid Waste 7
3. Gaseous Emissions 7
4. Costs and Energy Use 9
B. CHANGES IN PRODUCTION OF ALUMINUM 9
1. Air Pollution 9
2. Liquid and Solid Waste 9
3. Costs and Energy Use 11
4. Practices or Processes Requiring Additional Research 11
III. INDUSTRY OVERVIEW 14
\
IV. COMPARISON OF CURRENT AND ALTERNATIVE PROCESSES 17
A. ALUMINA PRODUCTION 17
1. Status 17
2. Current U.S. Alumina Technology (Bayer Process) 18
3. Alternative Alumina Production Processes 23
vii
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TABLE OF CONTENTS (Cont.)
Page
3. Alternative Aluminum Production Processes 57
4. Summary of Production Costs and Energy Requirements
for Production of Aluminum 82
V. IMPLICATIONS OF POTENTIAL PROCESS CHANGES IN THE ALUMINA/
ALUMINUM INDUSTRY 83
A. PRODUCTION OF ALUMINA BY ACID LEACHING OF KAOLIN CLAYS 83
1. Impact on Pollution Control 83
2. Energy Requirements 85
3. Factors Affecting the Possibility of Change 86
B. PRODUCTION OF ALUMINUM BY THE NEW ALCOA PROCESS AND BY
THE RETROFITTING OF TITANIUM DIBORIDE CATHODES TO THE
CELLS 86
1. Impact on Pollution Control 86
2. Energy Requirements 88
3. Factors Affecting the Possibility of Change 89
C. AREAS OF RESEARCH 89
APPENDIX A - INDUSTRY STRUCTURE - ALUMINUM 90
APPENDIX B - PRESENT TECHNOLOGY 106
APPENDIX C - CURRENT POLLUTION PROBLEMS AND EFFECTIVENESS OF
AVAILABLE POLLUTION CONTROL TECHNOLOGY 119
viii
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LIST OF FIGURES
Number Page
IV-1 Hydrochloric Acid-Ion Exchange Process 24
IV-2 Nitric Acid-Ion Exchange Process 24
IV-3 Toth Alumina Process 41
IV-4 Alcoa Chloride Process (Assumed Scheme) 61
A-l Location of Alumina Plants and Aluminum Smelters in the
United States 91
A-2 U.S. Aluminum Production and Consumption - 1960-1975 100
A-3 Annual Average Price Aluminum - 1910-1974 104
B-l Bayer Process for Producing Alumina 107
ix
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LIST OF TABLES
Number Page
1-1 Summary of 1971 Energy Purchased in Selected Industry Sectors 3
II-1 Air, Water, and Solid Waste Streams From Base Case and Process
Modifications 8
II-2 Summary of Results of Process Options in the Alumina Industry 10
II-3 Summary of Results of Process Options in the Aluminum Industry
Based on Bauxite 12
II-4 Summary of Results of Process Options of Combined Processes in
Production of Aluminum 13
IV-1 Estimated Production Costs in "Existing" Bayer Alumina Plants,
1975 19
IV-2 Estimated Production Costs in "New" Bayer Alumina Plants, 1975 20
IV-3 Capital Investment Summary for Environmental Control in Alumina
Industry 22
IV-4 Annual Operating Cost Summary for Environmental Control in
Alumina Industry 22
IV-5 Energy Consumption Summary for Environmental Control in Alumina
Industry 23
IV-6 Estimated Production Costs for New Alumina Plant, 1975
(Hydrochloric Acid Leaching Process) 31
IV-7 Estimated Production Costs for New Alumina Plant, 1975
(Nitric Acid Leaching Process) 40
IV-8 Toth Chlorination Process Cooling Tower Slowdown Wastewater
Treatment Costs 45
IV-9 Air Pollution Control Costs for the Toth Alumina Process 46
IV-10 Estimated Production Costs for New Alumina Plant, 1975
(Clay Chlorination: Toth) 50
IV-11 Comparative Costs and Energy Consumption in the Alumina Industry 51
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LIST OF TABLES (Cont.)
Number Page
IV-12 Estimated Production Costs in Present Day Aluminum Plants, 1975
(Hall Process) 54
IV-13 Estimated Production Costs in New Aluminum Plants, 1975 55
IV-14 Capital Investment Summary for Environmental Control in
Aluminum Industry 58
IV-15 Annual Operating Cost Summary for Environmental Control in
Aluminum Industry 59
IV-16 Energy Consumption Summary for Environmental Control in
Aluminum Industry 60
IV-17 Alcoa Chloride Process Cooling Tower Slowdown Wastewater
Treatment Costs 66
IV-18 SO and HC1 Pollution Control Costs for Alcoa Chloride Process 67
IV-19 Estimated Production Costs for New Aluminum Plant, 1975 69
IV-20 Estimated Production Costs in Existing Aluminum Plant with
Titanium Diboride Cathodes, 1975 76
IV-21 Estimated Production Costs for New Aluminum Plant, 1975 81
A-l U.S. Alumina Plants 92
A-2 U.S. Aluminum Plants 93
A-3 U.S. Aluminum Smelters - Age and Technology 95
A-4 U.S. Aluminum Shipments by Market and Percent of Market 99
B-l Bayer Alumina Production Range of Requirements and Considered
Average Requirements 111
B-2 Hall-Heroult Aluminum Smelting Range of Requirements and
Considered Average Requirements 116
C-l Representative Composition of Red-Mud 121
C-2 Summary of Effluent Reductions Achieved for Bauxite Refinery
Process Wastes Using Best Practicable Technology Currently
Available 123
C-3 Summary of Waste Disposal Cost Data 124
xi
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LIST OF TABLES (Cont.)
Number Page
C-4 Costs of Various Alternatives for Fluoride Removal 132
C-5 Emission Factors for Primary Aluminum Production Processes 135
C-6 Summary of Air Pollution Characteristics and Control 136
xii
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ACKNOWLEDGMENTS
This study could not have been accomplished without the support of a
great number of people in government agencies, industry, trade associations
and universities. Although it would be impossible to mention each individual
by name, we would like to take this opportunity to acknowledge the particular
support of a few such people.
Dr. Herbert S. Skovronek, Project Officer, was a valuable resource to us
throughout the study. He not only supplied us with information on work
presently being done in other branches of EPA and other government agencies,
but served as an indefatigable guide and critic as the study progressed. His
advisors within EPA, FEA, DOC, and NBS also provided us with insights and
perspectives valuable for the shaping of the study.
During the course of the study we also.had occasion to contact many
individuals within industry and trade associations. Where appropriate we
have made reference to these contacts within the various reports. Frequently,
however, because of the study's emphasis on future developments with compara-
tive assessments of new technology, information given to us was of a confiden-
tial nature or was supplied to us with the understanding that it was not to be
credited. Therefore, we extend a general thanks to all those whose comments
were valuable to us for their interest in and contribution to this study.
Finally, because of the broad range of industries covered in this study,
we are indebted to many people within Arthur D. Little, Inc. for their parti-
cipation. Responsible for the guidance and completion of the overall study were
Mr. Henry E. Haley, Project Manager; Dr. Charles L. Kusik, Technical Director;
Mr. James I. Stevens, Environmental Coordinator; and Ms. Anne B. Littlefield,
Adminis trative Coordinator.
Members of the environmental team were Dr. Indrakumar L. Jashnani,
Mr. Edmund H. Dohnert and Dr. Richard Stephens (consultant).
Within the individual industry studies we would like to acknowledge the
contributions of the following people.
Iron and Steel; Dr. Michel R. Mounier, Principal Investigator
Dr. Krishna Parameswaran
Petroleum Refining: Mr. R. Peter Stickles, Principal Investigator
Mr. Edward Interess
Mr. Stephen A. Reber
Dr. James Kittrell (consultant)
Dr. Leigh Short (consultant)
xiii
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Pulp and Paper:
Olefins:
Ammonia:
Aluminum:
Textiles:
Cement:
Glass:
Chlor-Alkali:
Phosphorus/
Phosphoric Acid!
Primary Copper:
Fertilizers:
Mr. Fred D. lannazzi, Principal Investigator
Mr. Donald B. Sparrow
Mr. Edward Myskowski (consultant)
Mr. Karl P. Pagans
Mr. G. E. Wong
Mr. Stanley E. Dale, Principal Investigator
Mr. R. Peter Stickles
Mr. J. Kevin O'Neill
Mr. George B. Hegeman
Mr. John L. Sherff, Principal Investigator
Ms. Nancy J. Cunningham
Mr. Harry W. Lambe
Mr. Richard W. Hyde, Principal Investigator
Ms. Anne B. Littlefield
Dr. Charles L. Kusik
Mr. Edward L. Pepper
Mr. Edwin L. Field
Mr. John W. Rafferty
Dr. Douglas Shooter, Principal Investigator
Mr, Robert M. Green (consultant)
Mr* Edward S. Shanley
Dr. John Willard (consultant)
Dr.. Richard F. Heitmiller
Dr. Paul A. Huska, Principal Investigator
Ms. Anne B. Littlefield
Mr.. J., Kevin O'Neill
Dr. D. William Lee, Principal Investigator
Mr. Michael Rossetti
Mr. R. Peter Stickles
Mr. Edward Interess
Dr. Ravindra M. Nadkarni
Mr. Roger E. Shamel, Principal Investigator
Mr. Harry W. Lambe
Mr< Richard P. Schneider
Mr. William V. Keary, Principal Investigator
Mr. Harry W. Lambe
Mr. George C. Sweeney
Dr. Krishna Parameswaran
Dr. Ravindra M. Nadkarni, Principal Investigator
Dr. Michel R. Mounier
Dr. Krishna Parameswaran
Mr. John L. Sherff, Principal Investigator
Mr. Roger Shamel
Dr. Indrakumar L. Jashnani
xiv
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ENGLISH-METRIC (SI) CONVERSION FACTORS
To Convert From
To
2
Metre
Pascal
Metre
t Joule
Pascal-second
Degree Celsius
Degree Kelvin
Metre
Metre /sec
3
Metre
2
Metre
Metre/sec
2
Metre /sec
1) Metre3
•Ibf/sec) Watt
.c) Watt
Watt
Metre
Joule
3
Metre
Metre
Metre
Metre
Pascal-second
Newton
Kilogram
Kilogram
Kilogram
Kilogram
Kilogram
Kilogram
Multiply By
4,046
101,325
0.1589
1,055
0.001
t; - (tj -32;
^ = tp/1'8
IS. Ix
0.3048
0.0004719
0.02831
0.09290
0.3048
0.00002580
0.003785
745.7
746.0
735.5
0.02540
3.60 x 106
1.000 x 10~3
1.000 x 10~6
0.00002540
1,609
0.1000
4.448
0.4536
0.02916
1,016
1,000
907.1
1,000
Acre
Atmosphere (normal)
Barrel (42 gal)
British Thermal Unit
Centipoise
Degree Fahrenheit
Degree Rankine
Foot
Foot /minute
Foot3
Foot2
Foot/sec
Foot2/hr
Gallon (U.S. liquid)
Horsepower (550 ft-1
Horsepower (electric)
Horsepower (metric)
Inch
Kilowatt-hour
Litre
Micron
Mil
Mile (U.S. statute)
Poise
Pound force (avdp)
Pound mass (avdp)
Ton (assay)
Ton (long)
Ton (metric)
Ton (short)
Tonne
Source: American National Standards Institute, "Standard Metric Practice
Guide," March 15, 1973. (ANS72101-1973) (ASTM Designation\E380-72)
xv
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I. INTRODUCTION
A. BACKGROUND
Industry in the United States purchases about 27 quads* annually, approxi-
mately 40% of total national energy usage.** This energy is used for chemical
processing, raising steam, drying, space cooling and heating, process stream
heating, and miscellaneous other .purposes.
In many industrial sectors energy consumption can be reduced significantly
by better "housekeeping" (i.e., shutting off standby furnaces, better thermo-
stat control, elimination of steam and heat leaks, etc.) and greater emphasis
on optimization of energy usage. In addition, however, industry can be expected
to introduce new industrial practices or processes either to conserve energy
or to take advantage of a more readily available or less costly fuel. Such
changes in industrial practices may result in changes in air, water or solid
waste discharges. The EPA is interested in identifying the pollution loads of
such new energy-conserving industrial practices or processes and in determining
where additional research, development, or demonstration is needed to charac-
terize and control the effluent streams.
B. CRITERIA FOR INDUSTRY SELECTION
In the first phase of this study we identified industry sectors that have
a potential for change, emphasizing those changes which have an environmental/
energy impact.
Industries were eliminated from further consideration within this assign-
ment if the only changes that could be envisioned were:
• energy conservation as a result of better policing or "housekeeping,"
• better waste heat utilization,
• fuel switching in steam raising, or
• power generation.
*1 quad = 1015 Btu
**Purchased electricity at an approximate fossil fuel equivalence of 10,500
Btu/kWh.
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After discussions with the EPA Project Officer and his advisors, industry
sectors were selected for further consideration and ranked using:
• Quantitative criteria based on the gross amount of energy (fossil
fuel and electric) purchased by industry sector as found in U.S.
Census figures and from information provided from industry sources.
The aluminum industry purchased 0.59 quads out of the 12.14 quads
purchased in 1971 by the 13 industries selected for study, or 2.2%
of the 27 quads purchased by all industry (see Table 1-1).
• Qualitative criteria relating to probability and potential for proc-
ess change, and energy and effluent consequences of such changes.
In order to allow for as broad a coverage of technologies as possible, we
then reviewed the ranking, eliminating some industries in which the process
changes to be studied were similar to those in another industry planned for
study. We believe the final ranking resulting from these considerations identi-
fies those industry sectors which show the greatest possibility of energy con-
servation via process change. Further details on this selection process can be
found in the Industry Priority Report prepared under this contract (Volume II).
On the basis of this ranking method, the aluminum industry, exclusive of
the mining aspects, appeared in sixth place among the 13 industrial sectors
listed.
C. CRITERIA FOR PROCESS SELECTION
In this study we have focused on identifying changes in the primary pro-
duction processes which have clearly defined pollution consequences. In select-
ing those to be included in this study, we have considered the needs and lim-
itations of the EPA as discussed more completely in the Industry Priority Report
mentioned above. Specifically, energy conservation has been defined broadly to
include, in addition to process changes, conservation of energy or energy form
(gas, oil, coal) by a process or feedstock change. Natural gas has been con-
sidered as having the highest energy form value followed in descending order
by oil, electric power, and coal. Thus, a switch from gas to electric power
would be considered energy conservation because electric power could be gen-
erated from coal, existing in abundant reserves in the United States in com-
parison to natural gas. Moreover, pollution control methods resulting in energy
conservation have been included within the scope of this study. Finally,
emphasis has been placed on process changes with near-term rather than long-term
potential within the 15-year span of time of this study.
In addition to excluding from consideration better waste heat utilization,
"housekeeping," power generation, and fuel switching, as mentioned above, cer-
tain options have been excluded to avoid duplicating work being funded under
other contracts and to focus this study more strictly on "process changes."
Consequently, the following have also not been considered to be within the
scope of work:
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TABLE 1-1
SUMMARY OF 1971 ENERGY PURCHASED IN SELECTED INDUSTRY SECTORS
SIC Code
Industry Sector
1. Blast furnaces and steel mills
2. Petroleum refining
3. Paper and allied products
4. Olefins
5. Ammonia
6. Aluminum
7. Textiles
8. Cement
9. Glass
10. Alkalies and chlorine
11. Phosphorus and phosphoric
acid production
12. Primary copper
13. Fertilizers (excluding ammonia)
1015 Btu/Yr.
3.49(1)'
2.96(2)
1.59
0.984(3)
0.63(4>
0.59
0.54
0.52
0.31
0.24
0.12(5>
0.081
0.078
-L1L VV LLJ_l_LI.
Industry Found
3312
2911
26
2818
287
3334
22
3241
3211, 3221, 3229
2812
2819
3331
287
(1)
(2)
(3)
(4)
(5)
Estimate for 1967 reported by FEA Project Independence Blueprint, p. 6-2,
USGPO, November 1974.
Includes captive consumption of energy from process byproducts (FEA Project
Independence Blueprint)
Olefins only, includes energy of feedstocks: ADL estimates
Ammonia feedstock energy Includedt APL eptimtes
ADL estimates
Source: 1972 Census of Manufactures, FEA Project Independence Blueprint,
USGPO, November 1974, and ADL estimates.
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• Carbon monoxide boilers (however, unique process vent streams yield-
ing recoverable energy could be mentioned);
• Fuel substitution in fired process heaters;
• Mining and milling, agriculture, and animal husbandry;
• Substitution of scrap (such as aluminum, iron, glass, reclaimed tex-
tiles, and paper) for virgin materials;
• Production of synthetic fuels from coal (low- and high-Btu gas,
synthetic crude, synthetic fuel oil, etc.); and
• All aspects of industry-related transportation (such as transportation
of raw material).
D. SELECTION OF ALUMINA/ALUMINUM INDUSTRY PROCESS OPTIONS
Within each industry, the magnitude of energy use was an Important criterion
in judging where the most significant energy savings might be realized, since
reduction in energy use reduces the amount of pollution generated in the energy
production step. Guided by this consideration, candidate options for in-depth
analysis were identified from the major energy consuming process steps with
known or potential environmental problems.
After developing a list of candidate process options, we assessed
subjectively
• pollution or environmental consequences of the process change,
• probability or potential for the change, and
4 energy conservation consequences of the change.
Even though all of the candidate process options were large energy users,
there was wide variation in energy use and estimated pollution loads between
options at the top and bottom of the list. A modest process change in a major
energy consuming process step could have more dramatic energy consequences than
a more technically significant process change in a process step whose energy
consumption is rather modest. For the lesser energy-using process steps process
options were selected for in-depth analysis only if a high probability for
process change and pollution consequences was perceived.
Because of the time and scope limitations for this study, we have not
attempted to prepare a comprehensive list of process options or to consider all
economic, technological, institutional, legal or other factors affecting imple-
mentation of these changes. Instead we have relied on our own background !
experience, industry contacts, and the guidance of the Project Officer and EPA
advisors to choose promising process options (with an emphasis on near-term
potential) for study.
-------
In our view, process changes in the aluminum .industry will be in response
to the four major problems confronting the industry today:
1. dependence on foreign sources of raw material;
2. heavy energy requirement at a time of rising energy costs;
3. rising pollution control costs; and
4. almost prohibitively high construction costs for new conventional
alumina and aluminum plants.
These problems will, in our view, lead to an emphasis on the following
new approaches:
• In Raw Material Preparation
1. There is growing industry interest in the possibilities of pro-
ducing alumina from domestic alumina-bearing raw materials—
alunite, kaolin, and anorthosite clays—and dawsonite, a sodium
aluminum carbonate mineral found in oil shale. The latter is
longer range since those who have investigated the possibility
of dawsonite as a. source of alumina from the industry have con-
cluded that this source will only be economic if the shale is
mined and retorted for its oil content, as a result of which
the residue would be a byproduct source of alumina. It cannot
be justified on the alumina content alone. However, clays are
more easily mined by simple surface methods and therefore con-
sidered as a potential shorter term source of alumina for reduc-
tion to aluminum.
Thus, with respect to alumina for aluminum production, we have
considered in this study three new process developments for pro-
ducing alumina from domestic clays as the alternative to the Bayer
process, which is not suitable for treating clays:
a) Nitric acid leaching process,
b) Hydrochloric acid leaching process, and
c) Clay chlorination such as the Toth alumina process.
The first two are considered because the U.S. Bureau of Mines
study of 23 identified processes and process variations for
producing alumina from domestic clays showed them to be the most
economic. We have also included clay chlorination, such as the
Toth alumina process, because we believe that it has merit and
might prove to be economical. Moreover, it might provide a
source of raw material for the Alcoa chloride process which uses
aluminum chloride as the feed to the cells.
-------
2. We have not considered the improvement of the thermal efficiency of
the Bayer process plants by increasing heat-transfer where surface
fouling occurs due to scaling of heat-transfer surfaces. This can be
improved by providing more heat exchangers to permit more frequent
cleaning of surface ara and better heat-transfer coefficients. This
does not qualify as a process change; moreover, the addition of more
heat exchangers will be made when justified by higher fuel costs.
We have not considered the installation of so-called fluid flash
calciners developed by Alcoa for calcining the product alumina
hydrate to alumina, and replacing the older, less efficient
rotary kilns that have been used. We did not consider it because
it is basically an equipment change and does not represent a
really significant effect on the total energy consumption (the
order of 1% of the total energy consumed to make aluminum from
its basic raw materials).
• In Aluminum Smelting
We considered the following as candidate process changes for the
production of aluminum that relate strongly to the problem of energy
conservation:
1. The Alcoa chloride electrolysis process; and
2. The application of titanium diboride cathodes to the existing
Hall-Heroult cells.
We have not considered other means of reducing the electrical consump-
tion from the considered average of 15,600 kWh/short ton to the best
known practice of about 12,000 kWh/ton in existing smelters. This is
attainable largely as a result of reducing the anode current densities
with an attendant reduction in the capacity of the cells which, of
course, means replacing existing small cells with large cells and
adding cell capacity, both of which would be very expensive. This is
discussed in Appendix B, but is not further considered in this study,
because it is not a process change but rather a change in equipment
and operations.
Recognizing that capital investments and energy costs have escalated rapidly
in the past few years and have greatly distorted the traditional basis for
making cost comparison, we believe that the most meaningful economic assessment
of new process technology can only be made by using 1975 cost data to the extent
possible. Consequently, in estimating operating costs we have developed costs
representative of the first half of 1975 using constant 1975 dollars for our
comparative analysis of new and current processes.
-------
II. FINDINGS AND CONCLUSIONS
A. PROCESS CHANGES IN PRODUCTION OF ALUMINA
1. Solid Waste
It is clear that more solid waste will be produced from treating clays to
recover alumina by any of the new processes - namely, nitric acid, hydrochloric
acid leaching, or clay chlorination - than is produced by the existing Bayer
alumina process. Since ba.uxite used in the Bayer process contains about 50%
alumina, while clay contains typically only 30-35% alumina, there is simply
more inert material. However, with the processing plant near the clay mines,
the waste can be returned to mined-out areas. In the case of a Bayer alumina
plant, the bauxite is imported and space must be found to dispose of the solid
waste ("red mud") from the process.
2. Liquid Waste
With respect to liquid waste, in the case of the nitric acid process the
liquid wastes will contain soluble nitrates, whereas with the hydrochloric acid
and clay chlorination processes, the wastes will contain soluble chlorides which
are generally less objectionable than soluble nitrates when discharged to the
water environment. If complete impoundment in an impervious barrier-lined
disposal area is required ("zero discharge"), the pollution control costs would
be greater for any of the clay-based processes than for the present Bayer
alumina plants.
3. Gaseous Emissions
The gaseous emissions from the existing Bayer alumina plants are minor,
limited largely to gaseous emissions from the boiler house, which would be S02,
depending on the fuel used and the dust from alumina and lime calcination, both
of which can be controlled to meet existing regulations.
In the case of the nitric acid and hydrochloric acid leaching processes,
the tail gases from the decomposition-acid recovery operation could contain
oxides of nitrogen and hydrogen chloride, both of which could be removed by
caustic scrubbing, but this would result in water-soluble nitrates and chlorides.
I
It would appear that more effective control, e.g., zero discharge, might
be necessary in the case of nitrates from the nitric acid process than might be
required for chlorides from the hydrochloric acid or clay chlorination processes
and for the solid and liquid wastes from the present Bayer -alumina process.
Table II-l qualitatively compares the air, water and solid waste streams
from the various process options considered.
-------
TABLE II-l
AIR, WATER, AND SOLID WASTE STREAMS FROM BASE CASE AND PROCESS MODIFICATIONS
Process Alternative
Alumina
Bayer (base case)
Hydrochloric acid
leaching
Nitric acid leaching
Clay chlorination (Toth)
Air Emission
• Dust from alumina
grinding
• Calciner flue gas
• Dust from alumina
grinding
• HCl-containing tail
gas from acid recovery
plant
• Calciner flue gas
(SO, + particulates)
• Nitrogen oxide -contain-
ing tail gas from acid
recovery plant
• Calciner flue gas
(862 and particulates)
• Tail gas exhaust from
chlorinator
• Flushing of chlorinator
purge material
Water Effluent Streams
• Thickener underflow
• Thickener underflow
• Scrubber water from
HC1 scrubbing waters
(caustic)
• . Thickener underflow
• Scrubber waters (caustic)
• Cooling tower blowdown
Solid Waste
Red mud
Waste clay
Waste clay
Waste clay
O3
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4. Costs and Energy Use
Table II-2 shows energy use and the cost of pollution control for produc-
tion of alumina. In the Bayer process both energy use and costs are small,
considering the present value of alumina at $125/ton and the projected cost of
more than $200.00/ton in new Bayer plants. The cost for complete environmental
control of the new clay-based leaching processes is estimated to be higher, but
not prohibitively high, considering the value of the product. The major environ-
mental cost in HNOg leaching involves SO? control, since coal is used as a fuel
source, while natural gas or low-sulfur fuel oil is the basis used for costing
the HC1 leaching process based on information available to us in early 1976.*
From a cost and energy viewpoint, the clay alumina process appears very
attractive. Thus future work on this process to verify the energy use and
economics assumed here bears watching.
B. CHANGES IN PRODUCTION OF ALUMINUM
1. Air Pollution
It seems likely that the Alcoa process and the use of titanium diboride
cathodes will reduce air pollution from the cells and from the anode—making
and -baking operations. In the case of the Alcoa chloride process, the anodes
will be inert, which means that anodes would be purchased rather than produced
at the plant. Thus, air pollution from anode-making in the Alcoa process would
be completely eliminated from the aluminum plant. When titanium diboride
cathodes are used, the fluoride emissions per ton of aluminum produced would
remain the same, but the gas volume to be scrubbed would be lower. Moreover,
we would expect less carbon monoxide emissions per ton of aluminum produced.
It would appear that costs for air pollution control from the cells and
cell rooms of the new Alcoa process and for the use of titanium diboride
cathodes in the Hall process would be less than the costs for the existing
process. The Alcoa process would be completely covered to recover chlorine
for reuse and, while there might be some losses of chlorine to the atmosphere,
controlling chlorine emissions to required-levels should.not be as difficult
as for fluoride emissions.
However, the Alcoa process would add a new source of gaseous emissions,
namely, sulfur from the coking step and hydrogen chloride from the chlorinator
tail gas. Of course, both can be' removed as required.
2. Liquid and Solid Waste
The use of titanium diborides would not significantly change the nature of
the liquid_ waste problem from the present operations. The new Alcoa process
If natural gas at $1.85/10^Btii in the HC1 leaching process could be replaced
100% by coal at $0.82/l06Btu, it would 1) decrease energy costs by about $39/ton
alumina, 2) increase pollution control,costs by about $25-30, and 3) result in
a net reduction of about $9-14/ton alumina.
-------
TABLE II-2
SUMMARY OF RESULTS OF PROCESS OPTIONS IN. THE ALUMINA INDUSTRY
(Basis: 700,000 annual tons alumina production)
Base Line
Clay
Bayer Process
. Units (New)
Production Facility
Capital investment
*
Production cost
Energy requirements
Environmental Control Facilities
Fixed capital investment
*
Operating cost
Energy requirements
Production plus Environmental
Control Facilities
Fixed capital investment
*
Total cost of production
Energy requirements
$106
$/ton
106 Btu/ton
$106
$/ton
106 Btu/ton
$106
$/ton
106 Btu/ton
280
235.37
14.53
0.89
1.40
0.056
280.89
236.77
14.59
Hydrochloric
Acid Leaching
430
320.72
39.21
0.28
5.00
0.016
430.28
325.72
39.23
Nitric Acid
Leaching
322
226.28
26.76
14.03
19.00
0.695
336.03
245.28
27.46
Chlorination
(Toth)
232.6
179.29
28.59
8.55
0.80
0.293
241.15
190.09
28.88
Includes pretax return on investment
-------
would introduce a new source of liquid and solid waste arising as a consequence
of bleeding off impurities from the electrolyte. This would consist of sludge
and sodium chloride.
3. Costs and Energy Use
The estimated cost of complete environmental control of aluminum plants is
a significant factor in both the capital and operating costs of aluminum
smelters. It amounts to about 9% of the investment and 3.7% of aluminum produc-
tion costs in new Hall plants, as shown in Table II-3.
Alcoa chloride process offers a potential route to making aluminum that
has energy savings of about 10%, while keeping operating costs the same or
slightly lower than for a plant based on Hall cell technology. Pollution control
costs are significantly lower because of the elimination of fluoride emissions.
Table II-4 shows that the combination of clay chlorination with the Alcoa
process results in significant cost savings. However, we recognize that addi-
tional research is required to prove out the economics of such a concept. Energy
use is comparable to the base line Bayer-Hall process combination.
4. Practices or Processes Requiring Additional Research
We believe that the EPA should review requirements for the Hall process and
look into possibilities for improving the capital and operating costs of the
pollution control systems used. We also suggest that the U.S. Government con-
sider the possibility of undertaking or sponsoring materials research in the
field of titanium diboride cathodes suitable in quality to permit long operating
life- in the Hall-Heroult cell environment. This development would have a
dramatic effect on energy savings in the aluminum industry. With minimal
capital charge requirement, such a development can be retrofitted to existing
aluminum plants. With lower power consumption and other things remaining equal,
there would be favorable environmental effects per ton of aluminum produced in
reducing the CO emissions from aluminum cells and emissions from power plants.
11
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TABLE II-3
SUMMARY OF RESULTS OF PROCESS OPTIONS IN THE ALUMINUM INDUSTRY BASED ON BAUXITE
(Basis: 160,000 annual tons aluminium)
Production Facility
Capital investment
A
Production cost
Energy requirements
Environmental Control Facilities
Fixed capital investment
*
Operating cost
Energy requirements
Production plus Environmental
Control Facilities
Fixed capital investment
Total cost of production
Energy requirements
Units
$106
$/ton aluminum
106 Btu/ton
$105
$/ton aluminum
106 Btu/ton
$10 6
$/ton aluminum
106 Btu/ton
Existing
Hall
140 (a)
698
187.82
28.48
44
1.71
168.48
742
189.53
Facility
Hall
with TlB2
182
696
151.18
29.90
37.2
1.31
169.90
733
152.49
New
Hall
(Baseline)
280
1,137
150.02
28.48
44
1.71
308.48
1,181
151.73
Plant
Alcoa
Chloride
280
1,107
135.10
4.23
16.5
0.42
284.23
1,123
135.52
Includes pretax return on investment
(a) Estimated undepreciated investment
(b) Estimated undepreciated investment with T162modification to produce 208,000 annual tons aluminum
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TABLE II-4
SUMMARY OF RESULTS OF PROCESS OPTIONS OF COMBINED PROCESSES IN PRODUCTION OF ALUMINUM
(Basis: 160,000 annual tons aluminum)
Base Line Alternative Process
Production Facility
Capital investment
Production cost
Energy requirements
Environmental Control Facilities
Fixed capital investment
Operating cost
Energy requirements
Production plus Environmental
Control Facilities
Fixed capital investment
*
Total cost of production
Energy requirements
Units
$106
$/ton
106 Btu/ton
$106
$/ton
10 6 Btu/ton
$106
$/ton
106 Btu/ton
Bayer Alumina
plus Hall (New)
403
1,372.37
164.55
29
46.72
1.77
432
1,419
166.32
Clay Chlorination
- Alcoa
296
1,032
160.24
12
37.35
0.99
308
1,069
161.23
Includes pretax return on investment
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III. INDUSTRY OVERVIEW
This chapter presents a general description of the aluminum industry;
further detail is provided in Appendix A.
The aluminum industry is comprised of two basic operations:
(1) the production of alumina from bauxite by the Bayer process, and
(2) the reduction of alumina to aluminum metal by the Hall-Heroult
electrolytic reduction process.
These two operations are conducted at entirely separate locations.
There are nine alumina plants within the United States. Six are located
on the Gulf Coast, because of requirements for receiving imported bauxite and
the availability of natural gas as a low cost fuel; two are in Arkansas,
originally for proximity to local bauxite deposits, which were the only major
domestic sources of bauxite in the United States; and one is in St. Croix, the
Virgin Islands. With the exception of the St. Croix facility, these plants are
all relatively old, the oldest having begun operation in 1940 and the rest in
the late *40rs and early '50rs. Individual plant capacities range from
1.385 million to 370,000 short ton/yr with the total U.S. capacity equal to
7.7 million short ton/yr. By modern standards these plants are small. Most
new installations being built abroad have a capacity of at least 1 million and
more typically 2 million short ton/yr.
The only domestic source of bauxite, the major raw material in the produc-
tion of alumina, is the Arkansas bauxite deposits. The U.S. industry has
always depended largely on imports for most of its supply of bauxite and alumina,
and as the quality of Arkansas bauxite has become poorer, this dependency on
foreign sources has increased. Primary sources of U.S. bauxite imports are the
Caribbean, northern South America, and Australia. Recent activity on the part
of source countries in the form of high levies on the bauxite exported and
organized pressure to carry out the alumina production in these countries have
placed substantial strain of the U.S. aluminum industry. For these reasons it
is unlikely that new Bayer alumina plants will be built in the United States.
However, if a successful process based on an alternative raw material is devel-
oped, such as a domestic clay-based process (as discussed in Chapter IV), we
could see new alumina plants being built in the United States. They would be
based on domestic alumina-bearing raw materials, principally the kaolin and
anorthosite clays, the use of which would promote some raw material independence.
14
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There are 31 aluminum smelters within the United States. These are owned
by 12 aluminum companies, six of which also produce alumina domestically.
These aluminum plants are located in three general areas:
• along the Mississippi and Ohio Rivers due to the availability
of low-cost coal as fuel and the transportation system provided
by the rivers;
• in Massena, New York, because of the St. Lawrence River transpor-
tation system and low-cost hydroelectric power; and
• in Washington, Oregon, and western Montana, also because of low-
cost hydroelectric power.
Half of the existing smelters have been in operation for 20 years. These are
both Soderberg and prebake smelters. Within the last 15 years, all smelters
that have been constructed have been prebake, because Soderberg smelters
require 2-10% more power. Total U.S. capacity is estimated at 5.019 million
short ton/yr; with individual plant capacities ranging from 285,000 short
ton/yr to 36,000 short ton/yr. Alcoa, Kaiser, and Reynolds are the largest
producers with Alcoa controlling 1.580 million ton/yr, Kaiser 724,000 ton/yr,
and Reynolds 975,000 ton/yr.
Through 1973 world consumption of aluminum experienced a long-term growth
rate on the order of 10% per year. U.S. consumption has risen gradually over
the years with the exception of a period during the 1940's when wartime need
for aircraft production caused a sharp rise in the curve. The building and con-
struction industries are the largest end-users of aluminum (22% of the market
in 1974), with transportation (18%), packaging (17%), electrical users (14%),
and consumer durable goods (9%) also playing major roles. Of these, packaging
and transportation are the fastest growing markets.
In the 1960's U.S. consumption grew by an averag "% per year (compared to
rates of 4-5% per year for steel and copper). Between i960 and 1970, the United
States' dominant position in terms of smelter capacity began to erode, falling
from 53% of the world total to 45%. The trend among U.S. producers to locate
a larger amount of their smelter capacity outside the "nited States continues;
15% is now located abroad.
The financial condition of the aluminum industry is a matter of growing con-
cern. The rapid rate of growth of the industry has generated heavy capital
requirements; the industry's requirement of $1.50-2.00 of capital investment per
$1.00 of annual sales is about three times the average for all industry. Since
a major share of the industry's capital is borrowed, the cost of money has had
a severe impact on aluminum costs.
Until recently there has been no incentive in the United States to reduce
power consumption. Aluminum smelters have traditionally been located in low-
cost electric power areas - in many cases a considerable distance from their
markets. Much of this power is hydroelectric, but with limited hydroelectric
resources to be developed in the United States, hydroelectric power is not
expected to.play a major role in the expansion of the United States aluminum
15
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industry. Thus, with no really cheap power left, freight costs, capital and
interest charges, and tariffs have become important site-selection factors.
Although the basic Hall-Heroult process for the reduction of alumina to
aluminum has not really changed since its introduction over 70 years ago,
important design and engineering changes have evolved. During the past 40-50
years commercial cells have increased in size more than threefold and have
diminished 35-40% in power consumption. Modern cell lines are more mechanized
and labor requirements in the cell rooms have been reduced to a minimum. In
the 1960's, costs were reduced about 10%, largely by reducing power consumption
through the use of larger cells with larger anodes, but it is likely that further
cost reduction in the 1970's will be limited.
The aluminum industry has grown rapidly by making metal available when it
was needed and at a price which made it economically attractive to users. If
supply is allowed to drop below demand for an appreciable period, list prices
will increase and some of the incentive to use aluminum would be lost. On the
other hand, the present downturn in demand has caused prices to weaken, despite
significant production cutbacks.
The industry is presently concerned that as the cost of power increases,
the cost and price of aluminum will increase and aluminum may lose some of its
share of the metals market to alternative materials. This is the reason for
the present research and development activity in the industry that has as its
objective reducing energy consumption, particularly in the smelting of alumina
to aluminum, where nearly all of the energy required to produce aluminum is
consumed.
In addition, there is growing interest in producing alumina from domestic
alumina-bearing raw materials, principally clays, to reduce the dependence on
imported raw materials. Their cost has been increasing, as mentioned earlier,
in spite of the fact that energy consumption is likely to be higher for producing
alumina from clays than for producing alumina from imported bauxite.
16
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IV. COMPARISON OF CURRENT AND ALTERNATIVE PROCESSES
The production of aluminum is and will continue to be a two-step opera-
tion consisting of:
1. Refining of alumina-bearing raw materials (bauxite or clays) to
high-purity alumina or possibly aluminum chloride; and
2. Conversion of high-purity alumina or aluminum chloride to molten
aluminum by high-temperature molten salt electrolysis.
In the recent past (1950fs to early 1960fs), there was much research and
development work done on the so-called "direct reduction" of alumina-bearing
raw materials to aluminum. Several alternative methods were considered, but
none showed any real promise and thus all have been abandoned. Based on these
very disappointing experiences, it is extremely unlikely that this activity
will be renewed.
A. ALUMINA PRODUCTION
1. Status
With respect to alternative process options for the first step in aluminum
production, i.e., the production of alumina, all present efforts in the United
States and other industrial countries are being directed toward recovering
alumina from alternative domestic alumina-bearing raw materials, largely clays.
The U.S. aluminum industry is based almost entirely on imported raw materials
in the form of bauxite or alumina. The threat of the formation of an inter-
national bauxite cartel by the bauxite-producing countries and the drastically
increased cost of these raw materials have made U.S. aluminum companies par-
ticularly interested in domestic clays as an alternative raw material. Kaolin
and anorthosite clays are available in abundance and at low cost in the United
States; in fact, a much lower cost, based on an alumina content, than imported
bauxite. No activity is currently being extended to developing an alternative
to the Bayer process for refining high-grade imported bauxite to alumina, nor
is there an incentive to do so. However, for a variety of reasons, there is
particular interest in production of alumina from the large reserves of kaolin
clay in Georgia and South Carolina.
Renewed interest in the technology and economics of producing alumina from
domestic raw materials has led the U.S. Bureau of Mines to undertake a program
to investigate the more promising clay-based processes in their laboratory at
Boulder City, Nevada. The Bureau recently estimated capital and operating costs
for a number of processes proposed for producing alumina from kaolin and anor-
thosite clays. Based on the Bureau of Mines' Information Circular 8648, pub-
lished in 1975, the following processes appear to have the lowest operating
17
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costs and therefore to be the most attractive: (1) the hydrochloric acid
leaching-liquid, ion exchange process, and (2) the nitric acid leaching-liquid
ion exchange process (developed by Arthur D. Little, Inc).
Interest continues in many of these leaching processes, in spite of the
prospect of higher energy consumption and higher capital costs than are required
for the construction and operation of Bayer alumina plants operated on imported
bauxite. In addition, the Toth alumina process, which involves production of
alumina and byproduct crude titanium dioxide by chlorination of clay in the
presence of carbon, appears to have potential merit and low costs, although
this process would have higher energy requirements than the Bayer process
(29 x 106 Btu for Toth vs 15 x 10& Btu for Bayer).
Accordingly, we have evaluated these alternative process options for the
production of alumina in terms of cost, energy requirements, .and effluents
produced. To achieve a meaningful evaluation, we have compared these processes
with the process presently being used to produce alumina in the United States
(the Bayer process). We have included the more prominent of the clay-basnd
processes, despite the fact that energy consumption is higher than that of the
Bayer alumina process for the following reasons:
(1) The aluminum industry is interested in these processes as a means
of limiting future escalation in prices of imported alumina or
bauxite;
(2) The U.S. Government is concerned with an increasing balance-of-
payments problem; and
(3) These processes have environmental implications.
2. Current U.S. Alumina Technology (Bayer Process)
At present, the sole technology used to produce alumina in the United
States is the Bayer process, which is discussed in detail in Appendix B. This
process is old and well developed, having first been introduced in 1888, but
it is applicable only to bauxite as the raw material. This process has the
ability to treat both trihydrate and monohydrate bauxites, although the cost
for treating monohydrate bauxite, used in European Bayer plants, is much higher.
Most of the Bayer plants located in the United States are old and largely
depreciated. These plants operate on the more easily treated trihydrate
bauxites imported from the Caribbean. Tables IV-1 and IV-2 show estimated costs
for both an existing plant and a new plant, based on the Bayer process. High-
lights of these tables are summarized below.
a. Costs
The average cost of alumina from an existing U.S. Bayer alumina plant is
estimated to be about $125/short ton of A^Oj. Capital costs for new Bayer
alumina capacity, as of March 1975, was about $400/ton of annual alumina
capacity. The nominal minimum economic size of a Bayer plant would be about
700,000 short ton/yr of alumina. Capital investment for this size installation
would be $280 million. Present costs for alumina, including return on invest-
ment, produced from a new Bayer installation, would be $237/short ton.
18
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TABLE IV-1
ESTIMATED PRODUCTION COSTS IN "EXISTING" BAYER ALUMINA PLANTS, 1975
Produce: Alumina
Process: Bayer
Annual Capacity: 700,000 net tons Capital Investment: (CI)*
Location: Texas
Annual Production: 700,000 net tons
VARIABLE COSTS
Raw Materials
• Bauxite
• Limestone
• Soda Ash
Energy
• Natural Gas
• Electric Power Purchased
• Misc.
Water
• Process
• Cooling
Direct Operating Labor (Wages)
Direct Supervisory Wages
Maintenance Labor (Wages)
Maintenance Supervision (Wages)
.Maintenance Materials & Supplies
Labor Overhead
Misc. Variable Costs/Credits
• Starch
TOTAL VARIABLE COSTS
FIXED COSTS
Plant Overhead
Local Taxes and Insurance
TOTAL PRODUCTION COSTS
Capital Charges
Pollution Control
TOTAL
Units Used in
Costing or
Annual Cost
Basis
Net ton
Net ton
Net ton
106 Btu
kWh
103 gal
103 gas
Man-hr
15% Op. Lbr
Man-hr
15% Mnt. Lbr
1.5% of RC
32% of wages
Net ton
i
60% of wages
2% of RC
5% of UI
$/Unit
23,00
5.00
68.00
0.70
0.014
0.50
0.05
6.50
6.50
180.00
Units Consumed
per Net Ton of
Product
2.40
0.133
0.075
11.64
275.00
2.00
2.75
0.88
0.80
0.006
$ per Net Ton of
Product
55.20
0.67
5.10
8.15
3.85
1.00
0.14
5.72
0.86
5.20
0.78
6.00
4.02
1.08
97.77
7.54
8.00
113.31
10.00
1.40
124.71
Undepreciated Capital Investment (UI) $140,000,000
Replacement Cost (RC) $280,000,000
19
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TABLE IV-2
ESTIMATED PRODUCTION COSTS IN "NEW" BAYER ALUMINA PLANTS, 1975
Product: Alumina
Process: Bayer
Location: Texa_s__
Annual Capacity: 700,000 net tons Capital Investment: (CI) $280,000,000 Annual Production: 700,000 net tons
VARIABLE COSTS
Raw Materials
• Bauxite
• Limestone
• Soda Ash
Energy
(a)
• Purchased Fuelv '
Fuel Oil or Gas
• Electric Power Purchased
• Misc.
Water
• Process
• Cooling
Direct Operating Labor (Wages)
Direct Supervisory Wages
Maintenance Labor (Wages)
Maintenance Supervision (Wages)
Maintenance Materials & Supplies
Labor Overhead
Misc. Variable Costs/Credits
• Starch
OTAL VARIABLE COSTS
IXED COSTS
Plant Overhead
Local Taxes and Insurance
Depreciation
OTAL PRODUCTION COSTS
Return on Investment (pretax)
Pollution Control
OTAL
Units Used in
Costing or
Annual Cost
Basis
Net ton
Net ton
Net ton
106 Btu
kWh
103 gal
103 gas
Man-hr
15% Op. Lbr.
Man-hr
15% Mnt. Lbr.
1.5* of CI
32% of wages
Net ton
60% of wages
27, of CI
7. 17. of CI
20% of CI
$/Unit
23.00
5.00
68.00
1.85
0.015
0.50
0.05
6.50
6.50
180.00
Units Consumed
per Net Ton of
Product
2.40
0.133
0.075
11.64
275.00
2.00
2.75
0.88
0.80
0.006
$ per Net Ton of
Product
55.20
0.67
5.10
21.53
4.13
1.00
0.14
5.72
0.86
5.20
0.78
6.00
4.02
1.08
111.43
7.54
8:00
28.40
155.37
80.00
1.40
236.77
(a)e.g., misc. chemicals, catalysts, supplies, services.
20
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b. Energy Consumption
The average energy consumption in Bayer alumina plants in the United
States is rather moderate, amounting to 275 kWh and 11.64 x 10^ Btu/ton of
alumina. On a fossil fuel basis (10,500 Btu/kWh), this amounts to 14.53 x
106 Btu/ton of alumina.
c. Effluent Control
Details of effluent control for the Bayer alumina plants are discussed
in Appendix C with investments and operating costs summarized in Tables IV-3
and IV-4, respectively. Details are discussed below:
(1) Water and Solid Waste
The first operation in the Bayer plant is the unloading of imported
bauxite, a partially dried bulk material consisting of both lump and fines.
Unloading is effected by normal grab bucket means, which is a possible but
minor point of air pollution, i.e., the dust is typically uncontrolled. The
bauxite carriers are primarily dedicated to the bauxite trade with minor back-
haul opportunity limited to backhauling caustic or coal to the source, caustic
for Bayer plant operation at the source> and coal as fuel for the foreign
Bayer plant operations. In either case, there is no need to clean the holds
before loading either coal or caustic solution.
The principal waste streams from the Bayer alumina plants are a red mud
stream, spent liquor purges, steam condensate, barometric condenser and other
indirect cooling water systems, and storm water run-off. Of these, the red
mud solid waste in slurry form is by far the most important, because it is the
major stream in terms of both solid and liquid wastes. The cost of achieving
zero discharge is largely the cost of red mud pond construction, piping, and
neutralization, and of other equipment necessary for proper operation of the
recycle system. The estimated water pollution control cost ranges from about
$0.30 to $0.60/ton of alumina, as detailed in Appendix C (Table C-3). For our
calculations here we use a figure of $0.48/ton of alumina, shown in Table IV-3
as amounting to $336,000 for producing 700,000 tons of alumina per year.
(2) Air
Emissions to the atmosphere cbnsist entirely of dust from the following
operations: grinding bauxite and calcining alumina and limestone. The latter
may or may not be carried out at the alumina plant. Emissions from these
sources are rather easily controlled at the source with air cleaning equipment
at an insignificant or relatively small cost.
(3) Energy
Energy requirements for pollution are shown to be about 0.06 x 10 Btu/ton
of alumina, as shown in Table IV-5, which is small compared to the" 14.5 x 106
Btu/ton of alumina used on the process side.
21
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TABLE IV-3
CAPITAL INVESTMENT SUMMARY FOR ENVIRONMENTAL CONTROL*
IN ALUMINA INDUSTRY
(Basis: 700,000 ton/yr alumina production)
Baseline Alternative Process
Bayer ' 11C1 HHO, Toth
Air Pollution Control Investments ($000)
Dust from alumina or clay grinding 85 175 — —
Flue gas from calciner
• participates 800 — '1,700 1,331
• S02 — — 12,200 6,588
HC1 from acid recovery — 100 — 276
NO from acid recovery — — 125 —
Total 885 275 14,025 8,195
Other pollution control costs — — — 355
TOTAL 885 275 14,025 8,550
Source: Arthur D. Little, Inc., estimates
Process solids and uasteuaters are discharged to a pond and are calculated as
an annual operating cost, instead of as a capital investment (see Table IV-4
and discussion in text).
**
Treatment of cooling tower bloudown (see Table 1V-8).
TABLE IV-4
ANNUAL OPERATING COST SUMMARY FOR ENVIRONMENTAL CONTROL
IN ALUMINA INDUSTRY
(Basis: 700,000 ton/yr alumina production)
Baseline Alternative Process
Bayer HC1 HN03 Toth
Water and/or Solid Pollution
Control Costs" ($000)
Ponding of process solids
5 wastewaters 336 3,260 1,810 1,444
Cooling tower blowdown 155
Total 336 3,260 1,810 1,599
Air Pollution Control Costs ($000)
Dust from alumina or clay grinding 52 110
Flue gas from calciner
• particulates 600 — 1,180 925
. S02 — — 10.200 *.790
HC1 from acid recovery — 85 — 231
NO from acid recovery — — 122 —
Total 652 195 11,480 5,946
Uait cost, $/ton Alumina $1-40 $5.00 $19.00 $10.80
Includes 20Z return on capital invested (see text)
22
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TABLE IV-5
ENERGY CONSUMPTION SUMMARY FOR ENVIRONMENTAL CONTROL
IN ALUMINA INDUSTRY
(Basis: 700,000 ton/yr alumina production)
Base Line Alternative Process
Bayer HC1 HN03 Toth
Water Pollution Control
Electric power, 106 kWh/yr 0.052 0.23 0.13 0.048
Air Pollution Control
Electric power, 106 kWh/yr 3.7 0.822 46.2 19.5
Total Electric Power, 106 kWh/yr 3.752 1.052 46.33 19.55
Total Fuel Equivalent* 106 Btu/yr 39,396 11,046 486,500 205,275
Unit Energy Consumption, 0.056 0.016 0.695 0.293
10b Btu/ton alumina
Source:- Arthur D. Little, Inc. estimates
@ 10, 5 00 Btu/kWh
3. Alternative Alumina Production Processes
a. Hydrochloric Acid Ion Exchange Process
Briefly, in the hydrochloric acid ion exchange process, clay is dehy-
drated, leached with hydrochloric acid, and then settled to separate the
residue from the aluminum chloride/iron chloride solution. This solution
is .then purified with an amine ion exchange system operation to remove the
iron chloride, while leaving the aluminum chloride in solution. The aluminxm
chloride in the solution is crystallized from the solution and decomposed to
alpha alumina, and the acid value is recovered. Details are described below
and can be found in Figure IV-1.
(1) Leaching
Crushed, dehydrated clay is fed to leaching tanks operated at approxi-
mately 225 °F where the clay is leached with 20% hydrochloric acid for about
1 hour. During leaching, 87% of the alumina in the dehydrated clay reacts
to form aluminum chloride by the reaction:
6HC1 - 2A1C13
23
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HYDROCHLORIC ACID
r
WEAK ACI
L
HYDROCHLORIC ACID
TO AC1O RECOVERY
WASH ACID
WATER
1 Jill.
— ^-| LEACHING
WET SOLID
1
i | |
HcONCCMTnATlON - . »- ACID VAPOR TO
CONCCNTRATION +• ^^ n£COVERY
1
L^-l CRYSTALLIZATION 1.^ .
I
_^ CRYSTAL SEPARATION | 1 -^-| S^Era^RY [Z^,
1 |
|
H ACID VAPOR TO
ULlAJMi-v.il nuw ^- AC[0 RECOVERv
ALUMINA @ A|R EM!SSIONS
<^> WATER EFFLUENT
[t] SOLID WASTE
Figure IV-1. Hydrochloric Acid-Ion Exchange Process
DEHYDRATION
- WATER VAPOR
| THICKENING AND FILTRATION | 1—^- TAILINGS
fwl
>N REMOVAL | | »• WA
~~, Q]
I CRYSTALLIZATIOM |
| DECOMPOSITION
. ALUMINUM NITRATE.
SOLUTION
VAPORS TO
ACID RECOVERY
(I) AIR EMISSIONS
' fyb WATER EFFLUENT
fY] SOLID WASTE
Figure IV-2. Nitric Acid-Ion Exchange Process
24
-------
Also, according to the USBM, this solution contains about 85% of the iron
present in the dehydrated clay in the form of ferric chloride. The leaching
requires about 1% excess hydrochloric acid over that required for the various
reactions involved in the leaching.
After leaching, the slurry is pumped to covered thickeners where the
residue is separated from the solution. The solution is pumped to a surge
tank and the residues washed with weak hydrochloric acid in a four-stage
countercurrent washing thickener operation. Residue underflow from the
washing circuit contains about 50% solids which are pumped to filters, reslur-
ried with recycle waste water, and then pumped to a waste pond; finally, the
overflow from the washing circuit is pumped to the surge tank.
(2) Ion Exchange
Ferric chloride contained in the solution must be removed to prevent
contamination of the produpt. The solution from the surge tank in the leach-
ing section is pumped to a three-stage countercurrent liquid ion exchange
operation. Each stage is a mixer settler. The aluminum-iron containing
solution is pumped to the mixer at one end of the circuit, and contacted with
an amine kerosene alcohol liquid ion exchange mixture containing 4.7 volume
% secondary amine, 10% n-decyl alcohol, and 85.3% by volume crude kerosene.
This water-immiscible liquid is pumped to the mixer at the other end of the
circuit. The contact is approximately 1 volume of ion exchange mixture per
volume of iron-containing solution. All of the ferric chloride is transferred
to the ion exchange mixture with essentially no loss of hydrochloric acid or
aluminum chloride. The iron-free aluminum chloride solution is pumped to a
surge tank in the crystallization and decomposition section and the iron-
containing ion exchange mixture is pumped to a three-stage countercurrent
regeneration system in which each stage is also a mixer-settler. About one
ton of water per ton of ferric chloride is used to strip the ferric chloride
from the ion exchange mixture. During the ion exchange regeneration opera-
tions, approximately 0.2 gallon of ion exchange mixture per 1000 gallons of
feed solution is assumed to be lost to the purified aluminum chloride solution
and the aqueous ferric chloride strip solution. Ion exchange mixture and
makeup are recycled to the ion exchange circuit for reuse. The ferric chloride
removed during regeneration is pumped to the waste decomposition section. The
ultimate disposition of the lost ion exchange medium is discussed below.
(3) Crystallization and Decomposition
Iron-free aluminum chloride solution is pumped from the surge tank to the
evaporators where the solution is concentrated. The vapor containing a small
quantity of hydrochloric acid is condensed and recycled to the residue washing
circuit in the leaching section. Concentrated solution from the evaporators
is pumped from a surge tank where it is mixed with mother liquor recovered
from aluminum chloride crystal separation. The solution is then pumped from
the surge tank to crystallizers where aluminum chloride in the solution is
crystallized as aluminum chloride hexahydrate by driving off water and hydrogen
chloride. Vapor from the crystallizers is condensed and then pumped to the
acid recovery section. The aluminum chloride hexahydrate is pumped from the
25
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crystallizers as a 35% solids slurry to continuous centrifuges where the
crystals are separated from the mother liquor and are washed with 34% hydro-
chloric acid. Mother liquor and washings flow to a sump from which most of
the solution is recycled to the surge tank feeding the crystallizers. To
prevent a buildup of impurities and the crystallization of some impurities
that would contaminate the product, part of the solution from the sump (1-2%,
depending on the level of contaminants in the feed) is pumped to the waste
solids decomposition section.
Aluminum chloride hexahydrate crystals recovered in the centrifuges are
conveyed to fluidized bed reactors operated at 2000°F where the crystals are
decomposed to alpha alumina, hydrogen chloride, and water vapor as shown in
the reaction:
2(A1C13 ' 6H20) - a A1203 + 6HC1 + 9H20.
The alpha alumina is cooled and conveyed to silos where it is stored until
shipped, and vapors from the kiln are fed into the acid recovery section.
(4) Waste Solids Decomposition
Mother liquor purged from the crystallization and decomposition sections
is fed directly to a crystallizer where acid vapor is driven off. This
results in the crystallization of most of the aluminum chloride and impurities
in the solution. Crystals are removed from the crystallizer and are fed to
rotary kilns operating at 2000°F where the crystals are decomposed to yield
acid which is sent to the acid recovery section. Acid vapors from the crys-
tallizer are also condensed and sent to the acid recovery section.
A ferric chloride solution obtained from the regenerative operation in
the ion exchange section is pumped to a fluid bed roaster operating at 1800°F
where the ferric chloride reacts with water vapor to form ferric oxide and
hydrogen chloride, according to the reaction:
2FeCl3 + 3H20 - Fe2°3 + 6HC1'
Vapor from the spray roaster is sent to the acid recovery section, while
the ferric oxide is cooled, mixed with recycle water from the waste pond and
waste solids from the waste decomposition kiln, and pumped to the waste pond.
This discarded solid waste material will contain undecomposable soluble
chlorides such as chlorides of the alkali and alkali earth metals that can
originate from the ore.
The small amount of organic amines, alcohols, and kerosene ion exchange
medium that is lost to primary purified aluminum chloride product solution,
or the stripped ferric chloride solution, would be largely steam-stripped i
during evaporation, ending up in the condensate from the evaporators. In the
case of both the aluminum chloride solution and the stripping liquor, these
materials would end up in condensed dilute hydrochloric acid, which goes to
26
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the residue washing end of the leaching circuit, thus to solids disposal.
In addition, some of the 0.2 gallon of ion exchange liquid lost per 1000
gallons of feed solution would be lost because of the polymerization in the
mixer settlers from which it has to be occasionally removed and incinerated
or dumped.
(5) Acid Recovery
Acid vapors from the crystallization and decomposition sections and from
the waste decomposition section are mixed with products of combustion from
which the acid must be removed. The acid streams are combined and fed to the
top of a cooler absorber, as is the 10% hydrochloric acid recycled from the
tailings tower. Approximately 34% hydrochloric acid is produced in the cooler
absorber and pumped to a surge tank. Lean gas from the cooler absorber is
fed to the bottom of the packed tailings tower where practically all of the
hydrogen chloride in the gas stream is absorbed by water to form a 10% hydro-
chloric acid solution. This 10% acid is pumped to the cooler absorber, while
the exhaust gas from the packed tailings tower is vented to the atmosphere.
This stream would require a caustic scrubbing system to remove any unabsorbed
hydrogen chloride vapors with the scrubber discharge added to the residues
discharged to the waste ponds.
Part of the hydrochloric acid produced in the cooler absorber is mixed
with a small quantity of water and is then recycled to the aluminum chloride
crystal washing operation in the crystallization and decomposition section.
The rest of the hydrochloric acid is mixed with acid condensate (obtained
from the crystallizers in the crystallization and decomposition section) and
the waste decomposition section water and makeup acid to form 20% hydrochloric
acid which is recycled to the leaching step.
(6) Status of the Process
The Anaconda Company operated a large-scale, pilot-plant operation using
hydrochloric acid leaching at Butte, Montana during the late 1950's and early
1960's. The firm produced moderate quantities of pot feed alumina that was
actually converted to aluminum in its aluminum smelter at Twin Butte, Montana.
In 1975 the U.S. Bureau of Mines tested this process, among others, at
its laboratory at Boulder City, Nevada. The test work, partly supported by
the aluminum industries, was carried out in a so-called mini-plant; i.e.,
a small integrated pilot plant. The results of this work have not yet been
published.
No commercial plant embodying this process ha,s ever been built and
operated.
27
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(7) Effluent Control
Water Pollution
The primary waste material from this process is the underflow from the
series of thickeners, which consists of the acid-insoluble clay fraction and
a dilute aluminum chloride aqueous solution which has a solids concentration
of approximately 50%.
Based on information from the U.S. Bureau of Mines, an anticipated composi-
tion for this sludge stream (for the 700,000-ton/yr base case plant) is as
follows:
Constituent Quantity (ton/day)
A1203 1,720
S±02 4,500
A1C13 (soluble) 91
Other soluble chlorides, Cl~ 200
Water 6,580
Other impurities 360
Total 13,451
This discharge is large, amounting to 6.7 ton/ton of alumina, nearly
50% of which is water. The major kaolin clay reserves are in the states of
Georgia (primarily), South Carolina, and Alabama. In these states the rainfall
exceeds the evapo-transpiration so that either water used for slurry transpor-
tation of the residues to the disposal pond would have to be eliminated, or
recycle water from the disposal lagoons would have to be used. Ideally,
recycle water from the disposal area should be used insofar as possible as
process water makeup to the plant. However, the extent to which this could
be accomplished is limited because of a soluble impurities buildup, as
discussed below.
In addition to the major components - alumina, silica and iron oxides -
the Georgia kaolin contains small amounts of calcium, magnesium, and titanium,
plus a small amount of vanadium as oxide, sodium, potassium, manganese,
phosphorous, zinc, lead, and tiny amounts of sulfur as sulfate, largely as
calcium or magnesium sulfates. Considering the above, one would expect that
soluble chlorides of calcium, sodium, potassium, zinc and lead might build up
in any recycle loop. A small amount of phosphoric acid would also be present.
Manganese would follow the iron and would be present in the solid tailings as
manganese oxides, as would be the case with the iron discharged. Thus, it is
doubtful that a completely closed-loop system would be possible. However, it
is entirely possible that a closed-loop water recycle system could be used for
transporting the solid residue to the disposal ponds by slurry.
-------
The pollutants of major concern are the soluble chlorides, which include
a number of the metals present in the clay. Because these wastes are acidic
and the liquid effluents have a high total dissolved solid content, it is
assumed that land disposal must be effected in an area where adequate provi-
sions have been made to prevent percolation into groundwater and run-off into
surface water. The most probable methods for disposal are either returning
the leached clays to the pits, or placing them in specially designed above-
ground impoundments. Although local geological conditions might permit return-
ing them to the pits, it has been assumed that an above-ground, diked impound-
ment lined with an impervious liner, such as an elastomer membrane, would be
used instead. Because the location of these alumina plants will be in geo-
graphical areas where the net rainfall exceeds the net evaporation, it will
be necessary to institute a careful water management program with the process
operation through recycle of water collected in the disposal logoons. When
a disposal lagoon is filled, it is expected that a ground cover would be
implaced to prevent leaching and lateral transport of water from rainfall.
This procedure would create a disposal cell in a form which should require the
least long-term management and with the high probability that all events, short
of catastrophic happenings, would not cause the materials to enter the water
environment. '
It is estimated that the annual production of solid waste could be con-
tained in an area 2050 x 2050 x 25 ft deep. The containing dikes would have
inner and outer walls sloping at 45-deg angles and a 40-ft wide roadway on
the top. It is estimated that the construction costs for such an impoundment
would be $3,260,000 as shown in Table IV-4, which is equivalent to $4.66/ton
of alumina. Because of the more elaborate construction envisioned as necessary
for impoundments holding these chloride wastes than is necessary for Bayer
process red-muds, the estimated solid waste disposal costs are significantly
greater than the $0.48/ton of alumina from the Bayer process.
Air Pollution
This process is based upon the leaching of clays, such as kaolin, which
generate as much dust as bauxite during grinding and initial calcination. The
process does generate several waste gas streams containing HC1. These are
sent to an acid recovery system where the HC1 is stripped. However, tail gas
from the acid recovery plant may contain small amounts of HC1. We assume that
controls are necessary, which would require a caustic/spray tower scrubbing
system, which should prove adequate, and the liquid discharge would go to the
tailings ponds.
Pollution Control Costs and Energy
As shown in Table IV-4, pollution control costs for the HC1 leaching
alternative are estimated to be $5/ton of alumina compared to $1.40/ton for
the Bayer process. Table IV-5 shows pollution control energy requirements
are small and amount to only 0.016 x 10^ Btu/ton of alumina.
-------
(8) Process Energy Use
This process consumes 134 kWh of power plus 37.8 x 10 Btu of fossil
fuel energy per ton of alumina, excluding the energy in the raw materials.
Converted to a fossil fuel basis, i.e., including the inefficiencies in power
generation (10,500 Btu/kWh) , the total energy consumption amounts to 39.21 x
10" Btu/ton of alumina, which is considerably higher than the Bayer process
in which the total energy consumption on a fossil fuel basis is only 14.53 x
Btu/ton of alumina.
(9) Capital and Operating Costs
We have reworked the Bureau of Mines ' estimate on capital costs by
updating these costs from the 1973 basis to an early 1975 basis, i.e.,
approximately March 1975. A 700,000-ton/yr alumina plant, based on the above-
described hydrochloric acid leaching process, would cost $430 million, i.e.,
$615/annual ton of capacity. This compares with a standard or conventional
Bayer plant cost (as of March 1975) of $400/annual ton of capacity. The
estimated operating cost per ton of alumina, including return on investment,
is shown in Table IV-6 to be $326/ton of alumina via the HC1 leaching process.
This compares unfavorably with existing Bayer alumina plants that can presently
produce alumina at $125/ton, and even new Bayer plants that can produce alumina
under present conditions at a cost of about $237/ton.
We have discussed the pollution control problems with the USBM personnel
presently involved actively in pilot plant work on this process and other clay-
based alumina processes. Their considered view is that all air streams con-
taining particulate or gaseous emissions should be treated, and all resulting
solid and liquid effluents should be discharged to a disposal area lined with
an impervious barrier with subsequent ground cover implacement, as discussed
and estimated above.
b. Nitric Acid Ion Exchange Process
Briefly, the nitric acid ion exchange process involves the following
steps (see Figure IV-2) :
1. Calcining the kaolin clay to make the contained alumina selectively
available for extraction with nitric acid;
2. Leaching the calcined clay with hot nitric acid at atmospheric
pressure to produce a solution of aluminum nitrate and a suspension
of the clay-insolubles ;
3. Separating the clay-insolubles from the aluminum nitrate liquor in
thickeners ;
4. Removing the iron and other impurities from the clarified aluminum
nitrate liquor by use of a liquid ion-exchange medium;
30
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TABLE IV-6
ESTIMATED PRODUCTION COSTS FOR NEW ALUMINA PLANT, 1975
(Hydrochloric Acid Leaching Process)
Product: Alumina
Process: Hydrochloric Acid Leaching Location: Georgia
Annual Capacity: 700,000 tons
Capital Investment: (CI) $430.000,000 Annual Production: 700.000 tons
VARIABLE COSTS
Raw Materials
• Clay (Kaolin)
• Hydrochloric Acid
Energy
• Purchased Fuel
- Natural Gas
• Electric Power Purchased
• Misc.
Water
• Process
• Cooling
Direct Operating Labor (Wages)
Direct Supervisory Wages
Maintenance Labor (Wages)
Maintenance Supervision (Wages)
Maintenance Materials
Labor Overhead
Misc. Variable Costs/Credits
• Organic Solvent
• Operating Supplies
TOTAL VARIABLE COSTS
FIXED COSTS
Plant Overhead
Local Taxes and Insurance
Depreciation
TOTAL PRODUCTION COSTS
Return on Investment (pretax)
Pollution Control
TOTAL
Units Used in
Costing or
Annual Cost
Basis
ton
ton
106 Btu
kWh
10;? gal
10J gal
Man-hr
15% Op. Lbr.
Man-hr
1.5% Mnt. Lbr.
2% of CI
32% of wages
I
Ib. •'
60% of wages
2% of CI
7.1% of CI
20% of CI
$/Unit
2.50
27.00
1.85
0.015
0.50
0.05
6.50
6.75
0.30
Units Consumed
per Net Ton of
Product
5.02
0.14
37.80
134.00
1.5
64.00
0.80
1.55
4.39
$ per Met Ton of
Product
12.55
3.78
69.93
2.01
0.75
3.20
5.20
0.78
10.08
1.51
12.29
5.62
1.32
2.40
131.42
10.54
12.29
43.61
197.86
122.86
5.00
325.72
31
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5. Removing the remaining impurities from the iron-free aluminum
nitrate liquor by means of vacuum crystallization of aluminum
nitrate nonohydrate;
6. Recovering the alumina by hydrolysis of the aluminum nitrate under
controlled conditions so that the nitrate values are recovered
largely as nitric acid rather than as nitrogen oxides;
7. Recovering the nitric acid and nitrogen oxide values in the form
of nitric acid for recycle; and
8. Calcining the product alumina.
A more detailed discussion of the process, presented below, is based on
extensive non-integrated pilot plant work, engineering experiments, and cor-
rosion tests.
(1) Clay Preparation
The raw material input to the process consists of the clay produced by
the mining and beneficiation of kaolin clay. Beneficiation consists of scrub-
bing the crude clay with water under agitation to thoroughly separate and
disperse the kaolin particles into the water leaving behind a sand fraction.
In this operation a hydroseparation takes place, and the kaolin is cleaned
and recovered by thickeners and filtration. The clarified water is recycled.
The washed clay is then extruded, dried, and fed to the calcination section
of the process. The sand, if high grade, is valuable; but if not, it can be
discharged to a designated site as a solid.
(2) Clay Calcination
The dried clay pellets are fed from a storage bin to a rotary kiln which
is equipped with attached planetary tube coolers. The burning zone of the
kiln is operated at 1475°F. The temperature of the discharged calcined clay
from the cooler is expected to be 190°F. Kaolin clay, when heated to 1475°F
for approximately one hour, loses its water of crystallization and the remain-
ing alumino-silicate structure undergoes a transformation which reorders the
aluminum and its associated oxygen atoms from their original regular sites in
the lattice to an amorphous alumina and a skeleton of crystalline silica.
Thus, more complete extraction of alumina is possible. Process steam is
produced from the 800°F off-gas. Coal is used as direct-fired fuel for this
step in the process. If high-sulfur coal is used, SCL scrubbing would be
required. Part of the ash from coal firing would drop out in the calcined
clay, but some fly ash would leave the kiln to be recovered from the off-gases
along with the fine particulate from the clay. This material could be dis-
charged dry to a designated disposal area or to residue disposal lagoons.
(3) Digestion
The calcined kaolin clay is charged to feed bins equipped with weight
feeders which discharge into agitated leaching reactors. These reactors are
constructed of titanium and operate at atmospheric pressure. They are vented
32
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through a reflux condenser in which the nitric acid vapors leaving the boiling
solution in the reactor are condensed and totally refluxed to the reactor.
However, the vents are manifolded to a vent line that goes to nitric acid
recovery to take care of any gases emitted during the filling and charging
operations.
The reaction which occurs between nitric acid and the alumina contained in
the calcined clay is exothermic. That heat is extracted from the leaching
reactors by letting the solution boil at atmospheric pressure and then con-
densing the vapors with return of the condensate. Therefore, the total heat
of reaction leaves the system in the cooling water from the condenser.
Digested slurry is pumped from the bottom of each reactor. Nitric acid
of sufficient concentration is metered directly from storage to each of the
reactors. The leaching system is batch, which is favored over continuous in
light of the important relationship between leach liquor composition and
leaching time.
(4) Separation and Thickening
The digested slurry is pumped to the continuous countercurrent separation
and thickening section. The thickeners would be 216 ft in diameter, concrete
lined with fiber glass cloth-reinforced, polyester-interior coatings. This is
based on a corrosion-materials of construction study.
An aqueous nitrate solution at any temperature above its crystallization
point contains a sufficiently high concentration of nitric acid to make it
corrosive, so that the heat exchangers interposed between the digesters and
the first thickener to cool the slurry from 280°F to 160°F must be made of
titanium to permit the use of the reinforced polyester in the first thickener.
The high temperatures of the leach slurry sent to the first thickener would
require a high cost lining since the first thickener will operate at a tem-
perature close to the feed solution temperature (160°F).
The underflow from each thickener is mixed thoroughly with the overflow
from the succeeding stages in agitated repulp tanks. The clarified overflow
of aqueous aluminum nitrate solution product from the first thickener is fed
through a surge tank to polishing filters before going to the purification
section.
I
The waste material from the underflow of the last stage thickener, which
consists of the acid insoluble clay fraction and a very dilute aluminum nitrate
aqueous solution, is filtered and the filter cake repulped with recycle water
and pumped to a lined storage lagoon.
(5) Purification
Iron and other impurities are extracted from the aluminum nitrate solution
in three countercurrently operated mixer-settler liquid ion exchange extraction
stages. The extractant is a di-2-ethylhexyl phosphoric acid (DEHPA) and tri-
butyl phosphate (TBP) solution in kerosene. The extractors are agitated
stainless-steel tanks. The settlers are made of the same material.
33
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The aqueous phase from the settler enters a surge tank and then proceeds
to the primary crystallizer where pure aluminum nitrate, Al (1^)3)3 • 9H20, is
produced, while the other cation impurities are rejected. The crystals are
separated from the mother liquor by centrifugation and sent on to the hydrolysis
step. The mother liquor is sent to a secondary vacuum crystallizer to produce
impure crystal which is recycled to the primary crystallizer with the iron-free
aluminum nitrate solution. A small bleed stream, is taken off at this point in
the process to remove soluble impurities. This stream also contains a small
amount of organic liquid, i.e., lost iron exchange, which can be skimmed from
the liquid if properly arranged or passed to the disposal lagoon.
The iron-loaded organic phase leaving the extraction goes to a spray tower
washing operation. There the small amount of nitrate which the DEHPA has
removed from the aluminum nitrate aqueous phase is extracted completely by
the water and discarded to the disposal lagoon, along with other solids and
liquids. The nitrate-free, but cation impurity-containing organic phase then
passes to a rubber-lined regeneration column where the organic liquid is con-
tacted with aqueous HC1 solution which strips the cations from the loaded
organic. The regenerated organic phase then passes to a water-wash spray
system where any small amount of contained hydrochloric acid is removed
before recycle. Now the regenerated nitrate- and chloride-free liquid ion
exchange organic is recycled for use again in the extraction area of the
purification section.
The aqueous phase leaving the liquid ion exchange regeneration column is
mixed with a small amount of 112804 in a reboiler of a Karbate HC1 distillation
column. A sulfate sludge containing sulfuric acid and ferrous sulfate waste
material is removed from the bottom of the agitated reboiler of this still,
while the overhead product (after condensation and partial reflux to the
distillation column) is HC1 of the proper concentration to be recycled for
reuse in stripping-regeneration of the liquid ion exchange medium. The sludge
is then removed from the bottom still and sent to the disposal lagoon. A small
loss occurs at the liquid ion exchange medium, i.e., DEHPA, TBP, and kerosene.
This loss is due to polymerization in the extractors, which have to be cleaned
periodically and dumped or incinerated, if this is permissible. Other losses
are due to the various solutions, e.g., the purified aluminum nitrate and the
stripping solution in the liquid ion exchange regeneration.
In the case of organics lost to the purified aluminum nitrate solution,
the organics would leave the system in the second crystallizer blowdown stream
which, if properly designed, might permit skimming off the organic phase; alter-
natively the organics can be pumped to the disposal lagoon, along with the
residue and other wastes. In the case of organics lost to the hydrochloric
acid-stripping solution, they could be allowed to concentrate in this solution
until the buildup became sufficient to skim off the separated phase.
(6) Decomposition
The purified aluminum nitrate crystals produced by the crystallization
step are melted and then pumped as a 57% A1(N03)3 solution into the three
fluidized-bed hydrolysis reactors. These reactors are heated indirectly by
34
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means of a high-temperature, organic, heat-transfer medium through vertical
tubes located in the reactor vessels. The heat-transfer medium is heated
indirectly in separate furnaces directly fired by coal, or any other fossil
fuel, depending on its cost and availability.
This heat-transfer medium consists of thermally stable, heavy, aromatic
liquids contained in an entirely closed system. Over time, a small amount
.of cracking occurs and the resulting lower boiling liquids are bled from the
system and replaced with new material. During the infrequent bleed-off opera-
tion, the liquids are condensed and ultimately used as fuel; the hydrocarbon
gases would be banned, as they discharge from the condenser.
Since coal firing is used in this operation, provisions for fly ash
removal and SC>2 control must be made.if high-sulfur coal is used.
The fluid-bed reactors are arranged in parallel with regard to feed, and
in series/parallel on the fluidizing vapor side to minimize the volume of
initial fluidization vapor. The exit gas from the final two reactors passes
through a set of cyclones and a glass cloth filter used to remove the small
amount of alumina product elutriated from the beds in the form of a fine dust.
The ratio of product which is formed on the surface of alumina particles which
constitute the fluidized bed to the alumina product which leaves the reactor
in the form of fine particles in the exhaust gas can be varied over a wide
range by proper selection of the operating conditions of the system. There-
fore, provision is made for the removal of prills, which are produced by
accretion within the fluid bed, and their combination with the dust collected
by the cyclone and glass cloth filter. It is important to understand that
this reactor system is fluidized initially with steam and subsequently in
the two parallel upper beds with steam and nitric acid vapor, i.e., no non-
condensable gases. It is a hydrolysis that is occurring in this system, not
a decomposition. This makes possible better recovery of nitrate values as
condensable nitric acid, so that gaseous emissions of oxides of nitrogen are
very small.
The product alumina material is then mixed with a stream of 1830°F alumina
particles and the mixture is evenly distributed over the top layer of a packed
moving-bed reactor system. In passage down through this second reactor, the
remaining nitrate values (approximately 8% of the original nitrate) are lib-
erated from the alumina particles in the form of nitric acid and nitrogen
oxides. A small amount of steam purge is added to the bottom of the packed
bed reactor to continually sweep the nitrogen oxides from the bed and to
complete decomposition by the time the particles have reached the bottom of
the system. The oxides of nitrogen that are purged from these operations
with steam go to the nitric acid recovery system.
The solids outlet stream from the moving-bed reactor is passed over a
vibrating screen to separate the fine alumina product particles from the
coarser heat transfer medium. The coarser pebbles are conveyed to a packed
moving-bed pebble heater in which they are reheated to 1830°F for the recycle
again to the main bed decomposer.
35
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(7) Nitric Acid Recovery
The nitric acid vapors evolved from the fluid-bed hydrolysis section are
fed into a nitric acid concentrating tower. In view of the ubiquitous nature
of chlorine in mineral deposits and process water, as well as the use of
hydrochloric acid in the regeneration of DEHPA in this process, a means of
removing the chloride from the main process stream, in addition to the one in
the liquid ion exchange section, is required. This is done to ensure that
corrosion of the materials of construction due to nitric acid is not accel-
erated by the presence of a high chloride level.
This chlorine is removed from the system by taking a relatively small
side stream from the middle trays of the concentrating tower and passing it
through a reactor into which air with a trace of ozone is bubbled. The ozone
liberates free chlorine gas from the nitric acid water solution. The chlorine-
free nitric acid can then be returned to the next tray of the distillation
column. The resulting nitric acid goes to storage for subsequent recycle to
the digestion section.
Chlorine gas liberated by the ozone is scrubbed with caustic in a vent
scrubber. The nitrogen oxide leaving the moving-bed decomposer via the
cyclone and cloth filters, mixed with water vapor, is passed through a con-
denser from which a large portion of the nitrogen oxide is recovered directly
as nitric acid when it reacts with the water produced during condensation.
The remaining nitrogen oxides, now rich in NO from the reaction between N02
and H20, are added to the gases leaving the ammonia burner in the nitric acid
makeup plant. That combined gas stream goes to the absorption system for the
production of makeup nitric acid for the system. Makeup nitric acid could be
purchased or made from the oxidation of purchased ammonia. It is assumed
that, in the latter alternative, any in-plant nitric acid unit would be
equipped with pollution controls adequate to meet new stationary source
standards.
(8) Final Calcination
The alumina leaving the final decomposer is sent to a well-insulated
storage silo in which the phase transformation to alpha alumina occurs. This
phase transformation is exothermic. The final calcined alpha-alumina is
cooled to storage temperatures in a conventional facility used in Bayer alumina
practice.
(9) Status of the Process
During the late 1960's Arthur D. Little, Inc. carried out a non-integrated,
pilot-plant operation on the above-described nitric acid process. Moderate
quantities were produced for inspection by an aluminum producer and, based on
the chemical analysis of the product and consideration of the physical qualities,
it was considered adequate in quality to be considered pot feed alumina for the
Hall-Heroult process cells.
36
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In 1975 the U.S. Bureau of Mines tested this process, among others, at
its laboratory in Boulder City, Nevada. This test work, partly supported
by the aluminum industry, was carried out at a so-called mini-plant (small
integrated pilot plant). The results of this work have not yet been published.
(10) Effluent Controls
Water Pollution
The primary waste material from this process is the underflow from the
series of thickeners, which consists of the acid insoluble clay fraction and
a dilute aluminum nitrate aqueous solution having a concentration of approxi-
mately 50% solids, including the scrubber liquid effluent and liquid blowdown
streams identified above that would go to the disposal lagoon.
Based on pilot plant -data, the anticipated composition for this sludge
stream (for the 700,000-ton/yr base case plant) follows:
Constituent Quantity (ton/yr)
A12°3
3,392
A1(N03)3 (soluble) 145
Other soluble nitrates, NO. ions 164
Water , 3,563
Other impurities 168
Total 7,546
The discharge, although smaller than that for the hydrochloric acid proc-
ess, is still large and amounts to about 3.8 tons of waste material per ton of
alumina produced, nearly 50% of which is water. The major kaolin clay reserves
"are in the states of Georgia (primarily) , South Carolina, and Alabama. In these
states the rainfall exceeds the evapo-transpiration rate, so that either water
used for slurry transportation of the residues to the disposal lagoon would
have to be eliminated, or recycle water from the disposal lagoons would have
to be used. Ideally, recycle water from the disposal area should be used
insofar as possible as process water makeup to the plant. However, the extent
to which this can be accomplished is limited because, of soluble impurities
buildup, as discussed below. In addition to the three major components -
alumina, silica, and iron oxides - the Georgia kaolins will contain small
amounts of calcium, magnesium, titanium, sodium, potassium, manganese,
phosphorus, zinc, lead, and a tiny amount of sulfur as sulfate, largely as
calcium or magnesium sulfates, plus insoluble vanadium oxides. Considering
the above, one would expect that soluble nitrates of calcium, magnesium,
37
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sodium, potassium, zinc, and lead might build up in any recycle loop. A
small amount of phosphoric acid could also be present. Manganese would tend
to follow the iron and would be present, along with iron, as sulfate sludge
aqueous phase leaving the iron exchange regenerator column after treatment
with sulfuric acid. Thus, overflow water from the disposal pond would be
•ised to repulp the filter cake after the final washing thickener underflow
filtration to provide slurry transport of the solids discharge to the disposal
lagoon.
The pollutants of major concern are the soluble nitrates which include
the above metal nitrates from the metals present in the clay. Because these
wastes will be acidic and the liquid effluents will have a high total dissolved
solid content, it is assumed that land disposal must be into an area where
adequate provisions are made to prevent percolation into groundwater and run-off
into surface water. The most probable methods for disposal are to either
return the leached clays to the pits from which they were removed, or place
them in specially designed above-ground impoundments. Although local geo-
logical conditions might permit return to the pits, it has been assumed that
an above-ground, diked impoundment lined with an impervious liner, such as
elastomer membrane, would be employed. Because the location of these alumina
plants will be in geographical areas where the net rainfall exceeds the net
evaporation, it will be necessary to institute a careful water management
program with the process operation through recycle of water collected in the
disposal lagoons. When a disposal lagoon is filled, it is expected that a
ground cover would be implaced so as to prevent leaching and lateral transport
of water from rainfall. This procedure creates a disposal cell in a form which
should require the least long-term management and with the high probability
that events, short of catastrophic happenings, would not cause the materials
to enter the water environment. ,
It is estimated that the annual production of solid waste could be
contained in an area 1,540 x 1,540 x 25 ft deep. The containing dikes would
have inner and outer walls sloping at 45-deg angles and have a 40-ft wide
roadway on the top. It is estimated that the construction costs for such an
impoundment would be $1,810,000 (shown in Table IV-4), which is equivalent
to $2.58/ton of alumina. Because of the more elaborate construction envisioned
as necessary for impoundments holding these nitrate wastes than is necessary
for Bayer process red-muds, the estimated solid waste disposal costs are
significantly greater than the $0.48/ton of alumina from the Bayer process.
Air Pollution Considerations
The calcination of beneficiated clay pellets would not generate as much
particulate as the calcination of bauxite, but dust emission controls will
still be required for clay particulate as well as fly ash removal, since coal
could be used in the calcination kiln. If high-sulfur coal is used, SO
scrubbing would also be required.
This process also generates several waste gas streams containing oxides
of nitrogen. These are routed, manifolded, and lead to the acid recovery
section. The acid recovery section has a small vapor purge line which must
be scrubbed using dilute caustic; the'resultant streams go to the tailings
ponds.
38
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Pollution Control Energy Use
Table IV-5 shows that pollution control energy consumption is much
larger than for the other processes, largely because of the use of coal
and necessity for stack gas scrubbing.
(11) Process Energy Use
This process consumes 139 kWh of power plus 25.30 x 10 Btu of fossil
fuels, excluding the energy in the raw materials. Converted to a fossil fuel
basis, i.e., including the inefficiencies in power generation, the total energy
consumption amounts to 26.76 x 10^ Btu/ton of alumina, which is considerably
higher than for the Bayer alumina process in which total consumption on a
fossil fuel basis is only 14.53 x 10^ Btu/ton of alumina.
(12) Capital and Operating Cost
Capital cost estimates were originally made by Arthur D. Little, Inc.
in 1973. These costs were checked in detail and in many cases revised by a
major foreign aluminum producer who was interested in the process. These
costs have been updated by appropriate escalation factors to early 1975 costs.
The results check out reasonably close to the Bureau of Mines' estimates,
revised and updated to the same time.
For a plant producing 700,000-ton/yr of alumina, we estimate that the
capital costs would be $322 million, i.e., $460/annual ton of capacity.
The operating costs for a Georgia location based upon units costs, as
of March 1975, are presented in Table IV-7. The estimated operating costs,
including return on investment, add to $245/ton of alumina, which compares
unfavorably with existing Bayer alumina plants that can presently produce
alumina at $125/ton. This cost is about the same as that of new Bayer plants
that produce alumina under present conditions at a cost of about $237/ton.
c. Toth Alumina Process
The Toth Aluminum Corporation (TAG) has been developing a process for
the production of alumina and byproducts from clays and ferruginous bauxites.
The process involves the chlorination of alumina-containing raw materials in
the presence of carbon to produce aluminum chloride vapor and other volatile
chlorides. These are subsequently purified to eliminate other metal chlorides
and then oxidized to produce alumina and chlorine for recycle. It is proposed
that the process would produce as byproduct a crude titanium dioxide which
might be classed as rutile. Based on kaolin clays, the steps in the process
involve: (1) ore drying and calcination; (2) chlorination in which the
aluminum, titanium, and iron present in the ore are carried overhead as
volatile chlorides; (3) separation of the chlorides from the aluminum chloride
by fractional condensation and distillation; and (4) separate oxidation of
the iron, silicon, and titanium chlorides to their respective oxides for
recovery of chlorine for recycle. Finally, the aluminum chloride, after
separation, is also oxidized to produce alumina and to recover chlorine for
recycle. Details of the operation (see Figure IV-3) follow.
39
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TABLE IV-7
ESTIMATED PRODUCTION COSTS FOR NEW ALUMINA PLANT, 1975
(Nitric Acid Leaching Process)
Product: Alumina
Process: Nitric Acid Leaching
Location: Georgia
Annual Capacity: 700.000 tons
Capital Investment: (CI) $322,000,000 Annual Production: 700.000 tons
VARIABLE COSTS
Raw Materials
• Clay (Kaolin) .
• Nitric Acid
• Hydrochloric Acid
• DEHPA
Energy
• Purchased Fuel
Oil
- Coal
• Electric Power Purchased
• Misc
Water
• Process
• Cooling
Direct Operating Labor (Wages)
Direct Supervisory Wages
Maintenance Labor (Wages)
Maintenance Supervision (Wages)
Maintenance Materials
Labor Overhead
Misc. Variable Costs/Credits
• Operating Supplies
TOTAL VARIABLE COSTS
FIXED COSTS
Plant Overhead
Local Taxes and Insurance
Depreciation
TOTAL PRODUCTION COSTS
Return on Investment (pretax)
Pollution Control
TOTAL
Units Used in
Costing or
Annual Cost
Basis
ton
ton
ton
Ib
f
10° Btu
10 Btu
kWh
103 gal
10 gal
Man-hr
15% Op. Lbr.
Man-hr
15% Mnt. Lbr.
2% of CI
32% of wages
60% of wages
2% of CI
7.1% of CI
20% of CI
$/Unit
2.50
90.00
27.00
1.15
1.85
0.82
0.015
0.50
0.05
6.50
6.75
, Units Consumed
per Net Ton of
Product
3.83
0.148
0.020
0.352
1.30
24.00
139.00
1.40
84.00
0.93
0.98
$ per Net Ton of
Product
9.58
13.32
0.54
0.40
2.41
19.68
2.09
0.70
4.20
6.05
0^91
6.37
0.96
11.20
4.57
0.87
83.85
8.57
9.20
32.66
134.28
92.00
19.00
245.28
40
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RAW CLAY
c
°2
1 OXID;
FUEL »-
FUEL ^>
CARBON
2 P"
OEHYDf
I
CALCIM
1
CHLORI
-------
(1) Ore Drying and Calcination
The kaolin clay, which has a free moisture content of about 10%, is
crushed and screened to pass 1/4-in. screen size. The screened ore is then
dried, presumably in kilns or 'fluid-bed dryers operated at about 300°F. The
dried ore, still containing 5% moisture, is then calcined at 1290°F and
discharged hot to the chlorination reactors. All of these operations require
devices that will prevent the discharge of fine particulate to the environ-
ment. If high-sulfur fuel is used, the facilities have to be able to control
SC>2 emissions.
(2) Chlorination
In this operation, calcined ore is fed at 1290°F to fluidized bed chlo-
rinators operating at 1470°-1830°F where, in the presence of carbon, the ore
is chlorinated. The carbon can be petroleum coke or low-grade coal coked at
the lowest cost as the reducing agent. Chlorine to the chlorinators is
primarily recycled off-gas from the aluminum chloride, ferric chloride,
titanium tetrachloride, and silicon tetrachloride oxidations, and possibly
could contain some oxygen and nitrogen. Makeup chlorine is obviously required
as a result of losses from the system which amount to almost 2% of the chlorine
circulation. TAC has carried out its own research on this step in the opera-
tion, but it should be pointed out that commercial plants have been success-
fully operated to produce aluminum chloride and other metal chlorides by chlo-
rination in the presence of carbon under thermal and corrosive conditions
similar to those found in this step of the Toth process.
TAC indicates that the chlorination of silicon and iron can be suppressed,
but we believe that some iron, silicon, and even some sodium chloride is
carried over in the off-gases. TAC indicates that the net overall reactions
occurring in the chlorinator are endothermic, but proposes that heat can be
added by preheating the chlorine, and that part of the carbon present can be
burned to carbon dioxide by air or oxygen addition to make up any heat
deficiency.
(3) Recovery and Separation of the Chlorides
Chlorides that pass overhead are separated by a combination of fractional
condensation and distillation, followed by reoxidation of the separated frac-
tions. The temperature of the off-gas from the chlorinator falls between 1470°
and 1830°F. These gases are first cooled indirectly in a waste heat boiler
to about 480°F. The cooled gas stream is then scrubbed with recycled sodium
chloride-aluminum chloride-ferric chloride molten salt solvent at 300°F to
remove aluminum chloride and ferric chloride and any sodium chloride in the
gas stream. Thus, the remaining gas off the scrubber contains titanium
tetrachloride, silicon tetrachloride, and non-condensable gases—carbon
monoxide and carbon dioxide. Since carbon and reactants (titania, aluminum!,
silica, and iron) are always in excess, there would be little if any chlorine
breakthrough.
42
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The aluminum chloride, ferric chloride, and sodium chloride removed in
the scrubber are then passed to a distillation column operated under pressure
wherein the absorbed aluminum chloride and ferric chloride are separated by
distillation. Sodium chloride condensed in the scrubber is bled from the
system at this point, carrying with it some aluminum chloride and iron
chloride which is oxidized in a separate unit to iron oxide and aluminum
oxide, while the sodium chloride remains unchanged. This operation produces
chlorine for recycle, while the solids are discharged to disposal.
The aluminum chloride-ferric chloride vapors from the distillation
column are then fed to a second distillation column, also operating under
pressure, for the final separation of aluminum chloride and ferric chloride.
The aluminum chloride separated at this point is the product stream which is
subsequently oxidized to produce the product alumina and recycle chlorine.
Ferric chloride produced at the bottom of this column can be sold directly,
or can be sent to an oxidizer to recover the chlorine for recycle and oxides
of iron.
C4) Aluminum Chloride Oxidation
•Liquid aluminum chloride, the main product stream from the distillation
column, is vaporized with the vapor then oxidized in fluid-bed oxidizers
operated at about 1500°-1560°F. Oxidation is carried out with oxygen to
avoid contamination of the recycle chlorine with nitrogen. The oxidizer
off-gas is passed through cyclone separators for removal of solids. The off-
gas, essentially chlorine, is recycled back to the chlorinator.
(5) Titanium Tetrachloride and Silicon Tetrachloride Separation and Treatment
Off-gases from the aluminum chloride, iron chloride scrubber, which consist
essentially of titanium tetrachloride, silicon tetrachloride, carbon monoxide,
and carbon dioxide, enter refrigerated condensers where the titanium tetra-
chloride and silicon tetrachloride are condensed at about -22°F. Silicon
tetrachloride and titanium tetrachloride from this condenser are fed to a
distillation column for separation of the components. Separated chlorides
from the distillation column are oxidized to recover chlorine for recycle.
TAG is proposing to produce special silicas for sale, which may or may not be
possible. However, the oxidized titanium tetrachloride would be a crude
titanium dioxide which certainly could be sold. This crude TiO£ byproduct
would be equivalent in value to rutile.
(6) Current Status
This process is presently under development by the Toth Aluminum Corpora-
tion. The development work is being carried out on a small scale. We know
of no plans to build a large pilot plant, although TAG is actively promoting
and seeking sponsors for such a plant that would be designed to produce 90
ton/day of alumina. It is expected that this pilot plant would be supported
by the sale of byproduct crude titanium dioxide and special silicas produced
from the oxidation of titanium tetrachloride and silicon tetrachloride.
43
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(7) Effluent Control
Water
This is a dry process. The scrubbing media used are molten salt mixtures
that are products of the process and are subsequently separated. There are no
aqueous effluent process streams, except indirect cooling water requirements
for cooling of exothermic reactions. Thus, cooling tower blowdown is probably
most economically handled by treating it; costs are estimated in Table IV-8.
Air Pollution Considerations
Three potential emission streams (described below) are apparent from this
technology:
(a) The exhaust from the chlorinator, after cooling and scrubbing to
remove the chlorides, will contain CO, CC^, and probably traces of
HC1, if moisture, chlorine, the more volatile titanium, and silicon
tetrachlorides are present. We expect that some chlorinated
hydrocarbons would result from the chlorination of heavy volatile
material remaining in the coke. We would also expect that these
materials would be removed in the low-temperature condensation step
required to remove the titanium and silica tetrachlorides. When
these materials are oxidized to recover the chlorine values for
recycle, the chlorinated hydrocarbons are also destroyed at the
high-temperature conditions where these materials oxidize.
(b) The dry residue from the chlorinator contains the ash from the clay
and coke, alumina, and non-volatile chlorides of the alkali and
alkali earth metals present in the clay and coke ash.
(c) In separating alumina from A1C13 vapor and chlorine following oxida-
tion, residual chlorine and A1C13 may exit in the solid alumina.
The same may also occur in the oxidation of silicon and titanium
tetrachlorides.
We have assumed that the sources of chlorine emission would be controlled
because there is a real economic incentive to conserve it and to prevent escape
of this hazardous gas, although it is not a criteria pollutant.
The emission rates for this process depend upon purge and exhaust rates
which for the most part are unknown at present.
In a series of enclosed condensing and scrubbing steps, each of the
chloride constituents is removed, leaving an exhaust containing carbon
monoxide, carbon dioxide, hydrogen chloride, chlorine and potentially sulfur-
containing gases such as I^S, COS, etc. This stream could be burned in a CO!
boiler and then caustic scrubbed to remove hydrogen chloride or sulfur dioxide.
Estimated costs for air pollution control are shown in Table IV-9.
44
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TABLE IV-8
TOTH CHLORINATION PROCESS
COOLING TOWER SLOWDOWN WASTEWATER TREATMENT COSTS
(Basis: 700,000-ton/yr alumina production)
CAPITAL INVESTMENT - $355.000
VARIABLE COSTS
Operating Labor
(including suprvis + OHD)
Maintenance
(including labor + OHD)
Chemicals
• Sulfur Dioxide
• Lime
• Sulfuric Acid
Fuel
Electrical Power
Sludge Disposal
Annual Cost per Annual
Quantity Unit Quantity Cost
1,800 man-hr/yr $11.38/man-hr 20,485
68 ton/yr
72 ton/yr
34 ton/yr
48,300 kWh/yr
675 ton/yr
«a 10% solids)
$340/ton
$30.75/ton
$51.15/ton
0.012/kWh
$5.00/ton
23,120
2,215
1,740
580
3,375
TOTAL VARIABLE COST 51,515
FIXED COST
Taxes & Insurance (@ 2%)
Depreciation (@ Z-.l%)
TOTAL FIXED COST
TOTAL ANNUAL COST
RETURN ON INVESTMENT @ 20%
TOTAL
$ per ton of alumina
Notes: 1. Treatment costs are based on a cooling tower blowdown flow rate
of 0.9 10 gal/day (2% blowdown) and a chromium concentration of 30 mg/1.
2. Treatment consists of reduction followed by lime precipitation
and clarification.
45
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TABLE IV-9
AIR POLLUTION CONTROL COSTS FOR THE TOTH ALUMINA PROCESS
Units Used
in Costing
or Annual
Cost Basis
$/Unit
S02
Control'
HC1
Control
CAPITAL INVESTMENT (CI)
VARIABLE COSTS (S/yr)
Electric Power Purchased kWh
Labor Wages raan-hr
Supervisory Wages 15% labor
Maintenance, Labor, Super-
vision, Materials and Supplies 5% CI
Labor Overhead 32% vages
Chemicals
• Lime ton
• Soda Ash
Residue Disposal ton
Total
FIXED COSTS ($/yr)
Plant Overhead 60% wages
Local Taxes and Insurance 22 CI
Depreciation ' CI/14
TOTAL PRODUCTION COSTS
Return on Investment (pretax) 20% CI
TOTAL (S/yr)
TOTAL ($ per ton alumina)
0.012
6.50
30.75
5.00
$6,588,000
170,200
86,000
12,900
329,400
31,600
1,724,700
455.500
2,810,300
59,300
131,800
470,600
1,317,600
4,789,600
$6.84
$276,000
2,700
16,000
240
13,800
590
130,300
163,630
1,100
5,520
19,700
55,200
230,750
$0.33
Two solids streams require flushing to remove the chlorides. The chlo-
rinator purge is large, because the clay and coke ash must be rejected. Also-,
the alumina formed in the oxygenator has to be flushed. The exhaust contain-
ing the flushing agent (air, for example) and residual chlorine is scrubbed,
along with the flush exhaust from the chlorinator purge, and subsequently is
scrubbed again with caustic or lime.
Solid Waste and Liquid Waste Control
The major sources of solid, wastes are the discharge of inert material
from the chlorinator and solid wastes from the sodium chloride purge, which
contain iron chloride and some aluminum chloride, along with the sodium
chloride. This stream is oxidized to recover chlorine from the iron and
aluminum chlorides, leaving iron oxide, alumina, and sodium chloride as solid
wastes. This could be leached to remove the sodium chloride in a waste liquid
stream, but only if the alumina could be1 recovered for recycle by subsequently
removing the iron oxide by magnetic separation. The third potential waste
solids stream is the silica resulting from the oxidation of silicon tetrachloride.
All of these streams are likely to contain some soluble chlorides. These
materials could be removed as dry solids, but the soluble chlorides would be
eventually leached by rain into the groundwater.
46
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Probably the best way to handle such solid waste materials, along with
discharges from any caustic or lime scrubbers used to control chlorine or
hydrogen chloride emissions, is to dispose of these solid and liquid effluents
in a storage area or lagoon lined with an impervious elastomer membrane.
Our best estimate of the composition and volume of these liquid and solid
waste materials for a 700,000-ton/yr alumina production are as follows:
Constituent Quantity (ton/day)
A10 218
Fe2°3
Other
Soluble Chlorides, Cl
Water
Total
This discharge is smaller than that for the acid leaching processes,
amounting to only 1.8 tons of waste per ton of alumina, because the waste
is largely a dry material. Again, the most likely location for a clay-based
alumina plant would be in the kaolin belt of Georgia (primarily) , South
Carolina, or Alabama. In these states the rainfall exceeds evapo-transpiration
so that water used for slurry transportation of the residue to the disposal
pond would have to be eliminated, or recycle water from the disposal 'lagoons
would have to be used. Ideally, recycle water from the disposal area should
be used as process water makeup to the plant. However, the extent to which
this could be accomplished is limited because of soluble impurities buildup,
as discussed below.
In addition to the major components - silica, alumina, and iron oxides -
the kaolin clays contain small amounts of calcium, magnesium, titanium, sodium,
potassium, manganese, phosphorus?, ( zinc, lead, and tiny amounts of sulfur as
sulfate, largely as calcium sulfate, plus a small amount of vanadium as oxide.
Of these impurities it can be expected that the chlorides of calcium, magnesium,
sodium, potassium, lead, and manganese would remain largely in the residue from
the chlorination, or be separated out in the first condenser and be separated
from the aluminum chloride and ferric chloride in the first distillation dis-
charged with the higher boiling sodium chloride-containing fraction. The
vanadium tetrachloride separates out with the titanium tetrachloride . The
phosphorus separates as the trichloride with the silicon tetrachloride. The
vanadium remains as an oxide contaminant in the titanium dioxide. The phos-
phorus contained in the silicon tetrachloride volatilizes as oxide during
the oxidation of the silicon tetrachloride to silica to recover chlorine for
recycle. Therefore, the chlorine-containing off-gases from the silicon tetra-
chloride oxidation have to be scrubbed with water to recover the P2°5 as
phosphoric acid for disposal.
47
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Thus, a variety of soluble chlorides are present in the solid and liquid
waste streams to the disposal lagoon which build up in the system if water
from the lagoon is used as process makeup. The clarified water from the
lagoon, however, could be used to provide slurry transport of solids to the
disposal lagoon.
The pollutants of major concern are the soluble chlorides discussed above.
The wastes are acidic and the effluent, if transported by water slurry to the
disposal area, would contain a high total dissolved solids content. It is
assumed that land disposal would have to be made into an area where adequate
provisions are made to prevent percolation into groundwater and run-off into
surface water.
The most likely method for disposal is either to return the effluents to
the mined-out areas, or place them in specially designed above-ground impound-
ments lined with an impervious liner, such as an elastomer membrane. When a
disposal lagoon is filled, it is expected that a ground cover would' be
implaced so as to prevent leaching and lateral transport of water from rainfall,
This procedure would create a disposal cell in a form that would require the
least long-term management and with the high probability that events, short
of a catastrophic happening, would not cause the materials to enter the water
environment.
It is estimated that the annual production of solid wastes could be con-
tained in an area 1,370 x 1,370 x 25 ft deep. The containing dikes would have
inner and outer walls sloping at 45-deg angles and have a 40-ft wide roadway
on the top. It is estimated that the construction costs for such an impound-
ment would be $1,444,000 shown in Table IV-4, which is equivalent to $2.06/
ton of alumina. Because of the more elaborate construction envisioned as
necessary for impoundment holding of those chloride wastes than is necessary
for the Bayer process red-muds, the estimated solid waste disposal costs are
significantly greater than the $0.48 per ton of alumina from the Bayer process.
Pollution Control Energy
Table IV-5 shows that pollution control energy requirements of about
0.3 x 106 Btu/ton of alumina are much larger than for the Bayer process,
but still small compared with process energy requirements.
(8) Process Energy Use
f
This process consumes 333 kWh of power and 25.1 x 10 Btu of fossil
fuel^excluding the energy in the raw material. Converted to a fossil fuel
basis, i.e., considering the inefficiencies in power generation, the total
consumption amounts to 28.59 x 10^ Btu/ton of alumina. This is considerably
higher than the Bayer process in which total energy consumption on a fossil
fuel basis is only 14.53 x 106 Btu/ton of alumina.
(9) Capital and Operating Costs
The capital and operating costs are based on estimates made by Toth
Aluminum Corporation. We have checked the operating cost unit requirements
48
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and unit costs. .The unit requirements are consistent with those reported
by others for similar operations, i.e., from the production of aluminum
chloride and titanium tetrachloride. The capital costs are also based upon
information from TAG estimates for the first quarter of 1975 to which we have
added a small contingency. The resulting capital cost estimates are for a
plant based on the above-described process. Toth Aluminum Corporation
estimated it would cost-$205/annual ton of capacity. The estimate used in
the analysis is based on $331/annual ton of capacity. This would mean that
the capital costs would be lower than for a Bayer plant which for 700,000-
ton/yr capacity would cost $400/annual tons today.
The estimated operating cost per ton of alumina (including return on
investment) based on this process is shown in Table IV-10 to be $190.09/ton
of alumina with a credit for the byproduct titania produced and about $209
without the credit for byproduct titania. These estimated costs with byproduct
credit are higher than from existing Bayer alumina plants, presently estimated
to produce alumina at $125/ton and which are expected to feel the effects of
increasing bauxite costs. However, the.se costs compare very favorably with
estimates for producing alumina in any new Bayer plant installation in the
United States, expected to be about $237/ton of alumina.
d. Summary of Production Costs and Energy Requirements for Production
of Alumina
Table IV-11 summarizes the costs and the energy consumption (fossil fuel
basis) for producing alumina by the existing Bayer process and the alternative
hydrochloric acid and nitric acid clay leaching processes and the Toth chloride
alumina process based on clay as the raw material. These costs are compared
on the basis of new plants, since it is unrealistic to compare these new
process plants with existing Bayer plants which are largely depreciated.
49
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TABLE IV-10
ESTIMATED PRODUCTION COSTS FOR NEW ALUMINA PLANT, 1975
(Clay Chlorination - Toth)
Product: Alumina
Annual Capacity: 700.000 tons
Process: Clay Chlorination: Toth Location: Texas or Georgia
Capital Investment: (CI) $232,600,000 Annual Production: 700.000 tons
VARIABLE COSTS
Raw Materials
• Clay (Kaolin)
• Chlorine
• Oxygen
Byproduct Credits (Crude Ti02)
Energy
• Purchased Fuel
Coal
Coke
• Electric Power Purchased
• Misc.
Water
• Process
• Cooling
Direct Operating Labor (Wages)
Direct Supervisory Wages
Maintenance Labor (Wages)
Maintenance Supervision (Wages)
Maintenance Materials
Labor Overhead
Misc. Variable Costs/Credits
• Other Operating Supplies
TOTAL VARIABLE COSTS
FIXED COSTS
Plant Overhead
Local Taxes and Insurance
Depreciation
TOTAL PRODUCTION COSTS
Return on Investment (pretax)
Pollution Control
TOTAL
Units Used in
Costing or
Annual Cost
Basis
ton
ton
ton
ton
106 Btu
ton
kWh
10* gal
10* gal
Man-hr
152 Op. Lbr.
Man-hr
15% Mnt. Lbr.
2% of CI
32% of wages
60% of wages
2% of CI
7.1% of CI
20% of CI
$/Unit
2.5Q
125.00
12.00
332.00
0.82
35.00
0.015
0.50
0.05
6.50
6.75
Units Consumed
per Net Ton of
Product
3.00
0.04
1.31
0.058
8.45
0.64
333.00
0.80
20.25
0.72
1.05
$ per Net Ton of
Product
7.50
5.00
15.72
-19.26
6.93
22.40
5.00
0.40
1.01
4.68
0.70
6.83
1.02
6.62
4.23
5.90
74.68
T. 94
6.62
23.59
112.83
66.46
10.80
190.09
50
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TABLE IV-11
COMPARATIVE COSTS AND ENERGY CONSUMPTION
IN THE ALUMINA INDUSTRY
Base Line: Bayer Process
Variable and Fixed Costs
$/Net Ton
Total for process
1
Pollution control
TOTAL
Total production
Pollution control
TOTAL
New Bayer
235.37
1.40
236.77
Hydrochloric Nitric Acid
Acid Leaching Leaching
320.72
5.00
325.72
226.28
19.00
, 245.26
Toth
Alumina
179.29
10.80
190.09
Energy Consumption
106 Btu/Net Ton
New Bayer
14.53
0.06
14.59
Hydrochloric
Acid Leaching
39.21
0.02
39.23
Nitric Acid
Leaching
26.76
0.70
27.46
Toth
Alumina
28.59
0.29
28.88
Includes return on investment
51
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B. ALUMINUM PRODUCTION
1. Status
The alternative processes for the production of aluminum that are being
considered by the aluminum industry are those methods that will significantly
reduce the power consumption in the Hall-Heroult electrolytic reduction proc-
ess, which is presently used to produce all of the primary aluminum throughout
the world.
The matter of greatest concern to the aluminum producers in the United
States is the amount of power consumed in smelting alumina to aluminum in the
existing aluminum plants. This is a critical matter in view of the rising
cost of energy and power both in the United States and Europe. Historically,
because of the large amount of power consumed in the conversion of alumina
to aluminum, the industry has been located near sources of low-cost power.
Within the United States such sources are becoming harder to find. Unless
power consumption can be reduced, the growth in aluminum production in the
United States will be slower in the future.
As a result of this concern, Alcoa has developed a new aluminum chloride
electrolysis process that is expected to require less power than the present
Hall-Heroult process. This process is to be based on Bayer alumina converted
to aluminum chloride. One might ask why .not on alumina recovered as aluminum
chloride from clays by the Toth alumina process. The answer is that this
would present a logistics problem with respect to recycling chlorine from the
Alcoa chloride cells that would be required for the chlorination of clays to
produce aluminum chloride. Since it is costly to ship chlorine from the alu-
minum plant to the sources of the clay or clay to the aluminum plant, the
only potential application of these two processes in combination would be to
locate aluminum plants at the source of the clays. Unfortunately, low-cost
power is not generally available in these areas. Moreover, to do this would
mean concentrating the new aluminum plants near sources of clay which would
limit the application of this new technology to new plants. However, we have
considered the potential of this combination of the Alcoa process and Toth
alumina processes because it is possible that in the longer range future a few
aluminum plants might be located at the clay raw material sources. We believe
that this is not likely to happen in the near future because of the momentum
that is represented by the large existing system in the aluminum industry
which, for a long time, will continue to be based on imported alumina or baux-
ite converted to alumina in domestic Bayer alumina plants. Also the produc-
tion of alumina benefits from the scale of operations, i.e., normally one alu-
mina plant produces enough alumina to supply several smelters so that it is
likely to be more costly to match the size of the raw material recovery plant,
in this case aluminum chloride from clay, to that required for a single nominal-
sized aluminum smelter.
In addition to interest in the new Alcoa process, the U.S. aluminum
industry is showing renewed interest in the potential of so-called refractory
hard metal cathodes for reducing power consumption in the present Hall-Heroult
aluminum reduction cells. Therefore, we have considered this renewed develop-
ment because it represents an opportunity to retrofit cells in existing plants
to conserve energy.
52
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The Toth aluminum process has received a great deal of publicity. This
is not the Toth alumina from clay process described earlier, but another proc-
ess that has been under development by TAG for converting aluminum chloride
to aluminum metal. It represents a major departure from the production of
aluminum by electrolysis to a pyrometallurgical process. In the past, the alu-
minum producers have been interested in pyrometallurgical methods of producing
aluminum, but have shelved these older concepts, such as the Gross process on
which Alcoa spent a great deal of money and time. Also, Pechiney worked on
two pyrometallurgical processing methods that have long since been shelved.
The Toth aluminum process is the latest of these pyrometallurgical processes,
and it is the only one that has generated any current interest; therefore, it
is considered in this report.
We have, therefore, evaluated four alternative process options for alu-
minum production: 1) Alcoa chloride process, 2) Refractory hard metal cathodes,
3) Toth aluminum process, and 4) the combination of the Toth alumina process
producing aluminum chloride from clay as feed to the Alcoa chloride process.
2. Current U.S. Aluminum Technology (Hall-Heroult Process)
The existing technology for the production of aluminum is at present
entirely the Hall-Heroult electrolytic reduction process, discussed in detail
in Appendix B. This process is old and well developed, but is applicable only
to alumina as the raw material. While there are some variations in U.S. alu-
minum smelters as regards the size and amperage-carrying capacity of the cells
and the older Soderberg modification method of producing and consuming anode
carbon, the process used is basically the same Hall-Heroult method.
a. Costs
Average cost of aluminum produced from existing U.S. aluminum smelters
is estimated to be about $742/short ton of aluminum (see Table IV-12). Capital
costs for new Hall-Heroult aluminum smelter capacity as of March 1975 was
about $1750/annual ton of aluminum capacity (see Table IV-13). The nominal
size of a conventional aluminum smelter would be about 160,000 short ton/yr,
which is about average for the present smelters in the U.S. industry. Capital
investment today for this size installation would be about $280 million.
Present costs for aluminum produced from new Hall-Heroult smelter installa-
tions, including return on investment, would be $l,181/short ton.
b. Process Energy Consumption
The average energy consumption in Hall-Heroult aluminum smelters in the
United States is 15,600 kWh/ton with new plants projecting 12,000 kWh. In
addition, 24 x 106 Btu of fossil fuel are required per ton of aluminum. On
a fossil fuel basis, i.e., considering the inefficiencies of power generation,
the total energy consumption would be 187.8 x 106 Btu/ton of aluminum for old
plants and 150 x 106 Btu/ton for new facilities, not including the energy
inputs in the raw or consumable materials.
53
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TABLE IV-12
ESTIMATED PRODUCTION COSTS IN PRESENT DAY ALUMINUM PLANTS, 1975
(Hall Process)
Product: Aluminum
Annual Capacity: ifin,
Process:
Hall
Capital Investment(CI) :_*_
Location: Kentucky — Tennessee
Annual Production;100,000 tons
VARIABLE COSTS
Raw Materials
• Bayer Alumina
• Cryolite
• Aluminum Fluoride
Energy
• Purchased Fuel
Natural Gas
• Calcined Coke
• Pitch
• Electric Power Purchased
• Misc .
Water '
• Process
• Cooling
Direct Operating Labor (Wages)
Direct Supervisory Wages
Maintenance Labor (Wages)
Maintenance Supervision (Wages)
Maintenance Materials
Labor Overhead
Miscellaneous Variable Costs/
Credits
TOTAL VARIABLE COST
FIXED COST
Plant Overhead
Local Taxes and Insurance
TOTAL PRODUCTION COSTS
Capital charges
Pollution Control
TOTAL (S/ton)
TOTAL ($/lb)
Units Used in
Costing or
Annual Cost
Basis
Net ton
Net ton
Net ton
106 Btu
Net ton
Net ton
kWh
Man-hr
15% of Op. Lbr.
Man-hr
15% of Mnt. Lbr.
2.5% of RC
32% of wages
60% of wages
2% of UI
5% of UI
$/Unit
125.00
336.00
350.00
1.50
80.00
70.60
0.01
6.50
6.50
Units Consumed
per Net Ton
of Product
1.93
.035
.02
6.6
.52
.15
15,600.
3.5
4.5
$ per Net Ton
of Product
241.25
11.76
7.00
9.90
41.60
10.60
156.00
22.75
3.41
29.25
4.38
43.75
19.13
600.78
35.87
17.50
654 .15
43.75
44.00
741.90
0.37
*Est. Avg. Undepreciated Investment (UI) $140,000,000
1975 Replacement Cost (RC) $280,000,000
54
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TABLE IV-13
ESTIMATED PRODUCTION COSTS IN NEW ALUMINUM PLANTS, 1975
(Hall Process)
Producti Aluminum
Annual Capacity: 160.000 tons
Process; Hall
Location! Tennesa»» -
Capital Investment (CI)*: $280,000,000 Annual Production: it.a nnn
VARIABLE COSTS
Raw Materials
• Bayer Alumina
• Cryolite
• Aluminum Fluoride
Energy
• Purchased Fuel
- Natural Gas
• Calcined Coke
• Pitch
• Electric Power Purchased
• Miscellaneous
Water
• Process
• Cooling
Direct Operating Labor (Wages)
Direct Supervisory Wages
Maintenance Labor (Wages)
Maintenance Supervision (Wages)
Maintenance Materials
Labor Overhead
Miscellaneous Variable Costs/
Credits
TOTAL VARIABLE COSTS
FIXED COSTS
Plant Overhead
Local Taxes and Insurance
Depreciation
TOTAL PRODUCTION COSTS
Return of Investment (pretax)
Pollution Control
TOTAL
Units Used In
Costing or
Annual Cost
Basis
ton
ton
ton
106 Btu
ton
ton
kWh
Man-hr
15% Op. Lbr.
Man-hr
15Z Mnt. Lbr.
2.5* of CI
32X of wages
602 of wages
2Z of CI
7.1Z of CI
20Z of CI
$/Unit
125.00
336.00
350.00
2.00
80.00
70.60
0.012
6.50
6.50
Units Consumed
per Net Ton
of Product
1.93
• .035
.02
6.60
.52
.15
12,000.00
3.50
4.50
$ per Met Ton
of Product
241.25
11.76
7.00
13.20
41.60
10.59
144.00
22.75
3.41
29.25
4.39
43.75
19.14
592.09
35.88
35.00
124.25
787.22
350.00
44.00
1,181.22
55
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c. Effluent Control
(1) Air and Water
Details of effluent control for the Hall-Heroult aluminum smelters are
discussed in Appendix C. Below the situation is described with respect to
water, air, and solids contained therein.
The principal sources of wastewater from primary aluminum smelting are
effluents from wet scrubbers used on pot line and pot room ventilation, wet
scrubbers used on anode-baking furnace flue gas, and wet scrubbers used on
cast house off-gases. There is also cooling water used in casting, cooling
rectifiers, and boiler blowdown. The volume of these sources of wastewater
is related to the type of air pollution control system used for particulate
and fluoride control. If dry gas cleaning methods are used in which the alu-
mina ultimately fed to the cells is the absorbent used to remove pollutants
from pot room gas, there would be no fluoride-containing wastewater from pot
lines and pot rooms. However, the ability to-use dry scrubbing methods, i.e.,
alumina to recover fluorides and particulates, depends on crust-breaking pro-
cedures for. charging alumina feed to the pots. If the center crust-breaking
is used, i.e., breaking the crust along the center line of the cell, then the
cell can be tightly hooded and dry scrubbing used. If side-breaking technology
is used, it is more difficult to hood the cell tightly and, with secondary air
inflow, the choice is wet scrubbing. Side-crust breaking and alumina feeding
result in higher electrical efficiency relative to center-crust breaking and
are therefore the logical choices for energy conservation in the future. At
present, this method is less amenable to tight hooding and thus requires wet
scrubbing.
(2) Solid Waste
Minor amounts of solid wastes originate from handling the storage and
feeding raw and consumable materials (alumina, calcined coke, cryolite and
aluminum fluoride) brought into the smelter. Emissions of these materials are
largely in the form of dust from handling and feeding to the cells and to the
anode-making op er at ions.
However, rebuilding of cells is the major source of solid waste from an
aluminum smelter. When a cell reaches the end of its useful life and has to
be rebuilt, it is removed from the line and taken to the cell-reconditioning
shop where the old refractory lining, remaining cathode, and steel connector
bar are removed. The cell is then completely dismantled and rebuilt. This
operation generates a good deal of solid rubble a'nd waste solid materials.
Most of the refractory internals are impregnated with cryolite and aluminum
fluoride. These materials are typically leached to recover the fluorides for
reuse, before discharging the resulting inert refractory wastes to a suitable
disposal site. The resulting leach solution is subsequently treated to'recover
the fluorides for reuse.
For a complete control system for an aluminum smelter with a capacity of
160,000 ton/yr investments would be about $178 per annual ton of aluminum capacity
56
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for a prebake plant. Consequently, for a 160,000 ton/yr aluminum smelter,
the investment would amount to $28.48 million as summarized in Table IV-14.
Operating costs would be about $58 and, with an allowance for chemical
recovery, the net cost per ton of aluminum would be about $44 as shown in
Table IV-15.
(3) Pollution Control Energy
Table IV-16 shows energy requirements for pollution control to be about
1.7 x 10^ Btu/ton aluminum.
3. Alternative Aluminum Production Processes
a. Alcoa Chloride Process
Alcoa announced its new electrolytic chloride process for aluminum smelt-
ing in 1973 with plans for a 15,000 ton/yr demonstration unit to be built in
Palestine, Texas for a 1976 startup. However, it has not released much detail
publicly. We base our estimates on what we can surmise from its announce-
ments, on a review of the pertinent patents, on a review of the literature on
chlorination of aluminum ores, and on a consideration of possible tempera-
tures and compositions. We have compared the process with the existing Hall oxide
electrolytic route for producing aluminum from alumina, described briefly above
and in Appendix A.
Briefly, the Alcoa chloride process starts with pot feed alumina from the
Bayer process. Specifications call for a minimum purity of 99.426% alumina.
The limits on impurities are: Si02 - .025%; Fe203 - .03%; CaO - .06%; MgO -
.002%; NiO - .005%; CaO - .01%; Mn02 - .002%; Na20 - .4%; Ti02 - .005%; ZnO -
.02%; V205 - .002%; Cr203 - .002%; K20 - .005%; Li20 - .001%; and P205 - .005%.
This alumina is converted into aluminum chloride by chlorination in the pres-
ence of carbon to form volatile aluminum chloride. This, in turn, is purified
and fed to the electrolytic cells to produce molten aluminum at the cathode
and chlorine at the anode. The chlorine is recycled to the chlorination sys-
tem. Figure IV-4 presents our judgments of how the Alcoa process is being
designed to operate. The various steps in the operation of the Alcoa process
shown in Figure IV-4 are described below.
(1) Coking
While alumina is fed to the cop stage of a two-stage, fluid-bed coking
system, No. 6 fuel oil is fed to the bottom stage where it is coked to impreg-
nate carbon on the alumina. The top fluid-bed stage is operated at relatively
low temperatures to condense uncracked liquid hydrocarbons that come overhead
from the lower stage and to separate these condensable liquids from the non-
condensable gases. The top stage is equipped with cooling pipes inserted in
the bed to maintain a low temperature. The condensed, cracked hydrocarbon
liquids coat the aluminum particles.
The alumina then flows to the bottom fluid-bed stage, operated at 1,650°F,
where.the fuel oil is cracked and coked. About 70% of the carbon contained in
57
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TABLE IV-14
00
CAPITAL INVESTMENT SUMMARY FOR ENVIRONMENTAL CONTROL IN ALUMINUM INDUSTRY
Base line: Hall-Heroult Cells for Aluminum
Production basis, ton/yr aluminum
Water and/or Solids Pollution
Control Investments ($000)
Air Pollution Control
Investments ($000)
Particulates
S0_ control
HC1 control
Fluoride
TOTAL ($000)
Base line Alternative Process Combinatii
1 Exist ing Hal] 1
with TiB, New Alcoa
Cathodes AiCJ_3
160,000 208,000 160,000
* * 375
3,700
155
28,480 * 29,900
1
Toth Clay-
ALCOA Chloride
160,000
595
813
10,613
322
****'
160,000
390
28,480
29,900
4,230
12,343
28,480
28,870
Source: Arthur D. Little, Inc. estimates
All air, water, and solids pollution control costs in aluminum production are provided in this number.
-------
TABLE IV-15
ANNUAL OPERATING COST SUMMARY FOR ENVIRONMENTAL CONTROL IN ALUMINUM INDUSTRY
Base line: Hall-Heroult Cells for Aluminum
Bayer Process for Alumina
Combination'
Production basis, ton/yr
Water and/or Solids Pollution
Control Costs ($000)
Air Pollution Control Costs ($000)
Particulates
SO- control
HC1 control
Fluoride
TOTAL
Unit cost, $/ton Al
Base line Alternative Process
'Existing Hall „ AT '
. , ~. New ALCOA
with TiB0 „,, . ,
„ , , 2 Chloride
Cathodes
160,000 208,000 160,000
104
2,425
114
7,040 * 7,740 *
7,040 * 7,740 * 2,643
44. 37.20 16.50
Alternative
1
Toth Clay-
ALCOA Chloride
160,000
809
410
4,535
220
5,974
37.35
Processes
I
Bayer-
Hall/fieroult
160,000
148
287
7,040 *
7,475 *
46.72
Source: Arthur D. Little, Inc. estimates
*Includes air, water, and solids pollution control.
-------
TABLE IV-16
ENERGY CONSUMPTION SUMMARY FOR ENVIRONMENTAL CONTROL IN ALUMINUM INDUSTRY
Base Line: Hall-Heroult Cells for Aluminum
Bayer Process for Alumina
Base line
Hall
Alternative Processes
Combination Processes
EXi-!inT
-------
H2O
CTi
OFF-
TOO
CALC
HEA1
BAYER
AI203
NO. 6
FUELOIL
DRYER
CALCINER
850° C
3f>
XI
MIS
ni>
kS
DIZER
IER FOR
JG
i
COKING
SYSTEM
900°C
AI203
RECYCLE
AI203
OXYGEN
Cl
Al 203WITH
1 CARBON AND
MAKEUP
Cl -
NaCI , LiCI
MAKEUP
'
LEACH
FILTRATION
SYSTEM
'
NaCI .OTHER
IMPURITIES
IN SOLUTION
Al 2O3
NaC ,
IMPURITIES
OXIDIZER
850° C
2
1
1
t Al 203,
IMPURE
AICI 3
CHLORINATOR
SYSTEM
700°C
j
I
1
CO/C02/HCI
GAS
H20
j
HCI
ABSORBER
SYSTEM
Al CI3
ELECTROLYSIS
CELLS
700°C
SLUDGES
\
CO/C02/HCI
FOR
CLEAN UP
35% HCI
FOR
SALE
Al (LIQUID)
Figure IV-4. Alcoa Chloride Process (Assumed Scheme)
-------
the fuel oil is deposited on the alumina. This bottom bed is equipped with
heating fingers or tubes in which a portion of the cracked off-gas is burned
with the air to provide heat for coking and deposition of carbon on the alu-
mina. The off-gases from this combustion could contain sulfur (802) which would
have to be removed by scrubbing. Feed rates are such as to deposit on the
alumina a slight excess of carbon over the stoichiometric amount required to
remove the oxygen in the alumina and yield a mixture of primarily carbon diox-
ide with some carbon monoxide in the subsequent chlorination step.
(2) Chlorination
The alumina, with a slight excess of carbon over the stoichiometric for
removal of combined oxygen as carbon dioxide, then goes to the chlorination
system. Chlorination is carried out in a fluid-bed system operated at about
1,300°F in which the alumina is converted to volatile aluminum chloride in
non-condensable off-gases, primarily carbon dioxide and carbon monoxide (70-30
volume ratio). The off-gases from the chlorination also contain some hydrogen
chloride from the reaction of chlorine with the hydrogen adsorbed on the coked
alumina feed. The off-gases also contain sodium chloride vapor in an amount
equal to most of the sodium present in the alumina feed and perhaps some highly
volatile sulfur chlorides and some vanadium tetrachloride as well, introduced
into the system with the oil. However, we believe that a vanadium-containing
oil could not be tolerated in this process because tetrachloride would form
and condense with the aluminum chloride, subsequently contaminating the metal.
(3) Off-Gas Handling and Impurities Removal
The off-gases, primarily aluminum chloride, are then subjected to high-
temperature condensation which takes out sodium chloride, some aluminum chloride,
and unreacted alumina. This condensate is separated and then oxidized to
recover chlorine for recycle by oxidation of the aluminum chloride to alumina.
The resulting solid mass is then subjected to a water leach filtration circuit
to remove the soluble sodium chloride and recover alumina for recycle. The
leached salt solution would be a source of water pollution that would have to
be impounded. The recovered alumina is dried and calcined at 1,560°F, and then
recycled to the fluid-bed coking system described above. The major portion
of aluminum chloride is not condensed and passes through the high-temperature
condensation along with the gases that consist largely of carbon monoxide,
carbon dioxide, and hydrogen chloride. This gas is then subjected to a final
condensation at about 150°F to remove, as solid or liquid, aluminum chloride
which is the product feed to the electrolytic cells. The remaining noncon-
densable gases—carbon monoxide, carbon dioxide and hydrogen chloride—then
pass to an absorption system in which the hydrogen chloride is absorbed to
produce a byproduct 35% hydrochloric acid solution which is available for sale.
The off-gases from this scrubber would be burned, probably in a carbon monoxide
boiler, or flared.
(4) Cell Operations
( " ~
Cell electrolyte consists of 5% aluminum chloride and a mixture of sodium
chloride and lithium chloride. Both the cathode and anode are inert carbon
electrodes, i.e., non-consumable electrodes. Since they are inert, it is
62
-------
unlikely that either the anode or the cathode would be produced at the aluminum
smelter, but rather that they both would be purchased from the suppliers of
carbon electrodes.
Sodium aluminate tends to build up as sludge in the cell system. This
sludge must be removed periodically from the cell and, when removed, tends to
carry with it some electrolyte containing sodium chloride, lithium chloride,
and aluminum chloride. Thus there is a requirement for lithium and sodium
chloride make-up. The cells would be completely covered to recover the
byproduct chlorine from the anode and any aluminum chloride vapor from the
cell electrolyte. However, aluminum chloride vapor losses are expected to be
very small, because the vapor pressure of aluminum chloride is reduced to a
very low level as a result of the formation of a double salt with sodium
chloride which has a low-vapor pressure.
The cell operates at about 1,290°F, much lower than the 1,770CF average
for the Hall cells.. It is likely that the cells would operate at slight posi-
tive pressure to avoid air or water in-leakage which would be detrimental to
their operation by forming oxide sludge on the cathode; this would reduce the
current efficiency. It is likely that there would be some fugitive emissions
from these cells that are likely to be operated at slight positive pressure.
It is almost impossible to feed a solid, such as aluminum chloride, and elec-
trolyte make-up sodium and lithium chloride, or remove sludge from a closed
system under slight positive pressure without some fugitive gaseous emissions.
Some provisions would have to be made to ventilate the cell room to remove
chlorine and aluminum chloride, if present, by scrubbing the gas collected
through roof monitors.
The make-up requirements to the process are chlorine, sodium chloride,
and lithium chloride. Make-up chlorine is required because any hydrogen or
water entering the chlorinator forms HC1, which exits with off-gases and is
absorbed to produce an impure muriatic acid for sale as a byproduct. Sodium
and lithium chloride make-up is required to make up 'for losses or electrolyte
removed as sludge—largely sodium aluminate from the cell.
The advantages of the Alcoa chloride electrolysis relative to. the exist-
ing Hall oxide electrolysis appear to be the following:
• The electrical energy requirement is sharply reduced, because the
decomposition voltage and the bath resistivity are both lower for
the chloride melt;
• By eliminating oxygen from the system, the chloride process does
away with the need to continually fabricate and replace the consum-
able carbon anodes; instead, permanent graphite electrodes can be
used, and the expensive energy-consuming anode baking facilities
eliminated;
• Because electrodes can now be permanently emplaced, it is possible
to design chloride process cells with multiple sheet electrodes
stacked one above another (the so-called "multipolar" electrode
configuration) so that one cell then becomes the equivalent of sev-
eral single-cells, with consequent savings afforded by the much more
compact cell design;
63
-------
• The chloride cell operating temperature is about 1292°F rather than
than the 17426-1832°F temperature, of the Hall process;
• The fluoride emissions of the Hall process are completely avoided
since no cryolite or fluoride materials are used in the chloride
process. '
(5) Pollution Control
Water Pollution Considerations
Since alumina is the basic raw material for both the Hall process and the
Alcoa chloride process, those waterborne pollutants (heavy metals) emanating
directly from the alumina itself will be substantially the same for both proc-
esses. It is reasonable to expect that, as in the case of the existing process,
plants using the Alcoa chloride process will not have to. comply with specific
limitations on heavy metals.
Unlike the Hall process, the Alcoa chloride process does not use a
fluoride-containing fluxing agent, eliminates the fluxing agent, and consequently
eliminates the fluoride emissions. This feature represents a definite advan-
tag'e over the existing process in terms of water pollution control.
The Alcoa chloride process does, however, produce a chloride-containing
wastewater stream. In this process the bulk of the chlorine stream used in
the process is recycled. A small fraction of the chlorine is unavoidably lost
from the chlorine recycle loop and eventually enters the total wastewater
stream as chloride. A small amount of sodium ion (also inherent in the exist-
ing process) also comes in contact with water. Thus, the wastewater from the
Alcoa chloride process contains a quantity of sodium and chloride that is not
present in the wastewater from the existing process.
To assess the significance of the previously non-existent sodium chloride
wastewater Ipad, data from the NPDES discharge permit of the Alcoa demonstra-
tion plant in Palestine, Texas were examined, in conjunction with calculated
quantities of sodium chloride, and then extrapolated up to the base case
160,000-ton/yr aluminum plant. The following is our estimate of the sodium
chloride pollutional load for a 160,000-ton/yr plant.
• Wastewater flow rate = 1,230,000 gal/day;
• Total sodium chloride wasteload = 12,300 Ib/day;
• Sodium chloride concentration = 1,200 mg/1.
The above estimate represents the maximum quantity of sodium chloride
anticipated, as a definite fraction of sodium will leave the plant in the alu-
minum itself and be entrapped in the solid sludges removed from the cells. The
quantity and concentration of the sodium chloride permits discharge to receiv-
ing waters under the present effluent limitation guidelines. However, water
quality limitations for some locations may result in restrictions. For purposes
64
-------
of estimating wastewater pollution control costs, it has been assumed that
discharge to surface waters would be permitted.
During the chlorination part of the process, alumina, carbon (from cracked
No. 6 fuel oil), and chlorine are contacted in a fluidized state. It is pos-
sible that chlorine could react with certain residual hydrocarbon compounds to
form chlorinated hydrocarbons, a potential pollutant. If indeed this phenomenon
does occur and is found to be a serious problem, one possible solution is the
installation of a combustion chamber to incinerate the chlorinated hydrocarbons.
It is, however, quite possible that the Alcoa chloride process will actually
produce less waterborne organic pollutants than the existing process, due to
the elimination of the anode baking plants, since it employs non-consumable
graphite anodes. However, the Alcoa chloride process uses large volumes of
process cooling water. If the cooling water is recirculated through a cooling
tower, as is the conventional practice where large flow rates are included, a
small purge stream or blowdown will be discharged, as a wastewater effluent.
In such cooling water circuits, chromate corrosion inhibitors are often added
and will, therefore, be present in the cooling tower blowdown. If appreciable
amounts of chromates are used, the cooling tower blowdown will have to be sub-
jected to chromium removal prior to discharge.
Chromium removal involves two steps, reduction and precipitation. It is
necessary to first reduce chromium in the Ijexavalent form to the less toxic and
more easily removed trivalent form. The soluble chromium is then precipitated
from solution and separated from the liquid stream. Typically, sulfur dioxide
is used as the reducing agent and lime is used for the precipitation step.
The 160,000-ton/yr plant has a cooling water circulation rate of 53,000,000
gal/day. With a blowdown rate of 2%, the cooling tower blowdown flow rate would
be 1,060,000 gal/day. While the chromium concentration of the blowdown can
vary considerably, 30 mg/1 would be a typical concentration. By employing the
above treatment process, chromium concentrations of less than 0.1 mg/1 could
be,achieved. Cost estimates for such a chromium treatment system are presented
in Table IV-17.
Air Pollution Considerations
Because of the hazards of working with chlorine, the gas systems would of
necessity be quite tight. After solids recovery, there are two potential
emission sources which would require treatment:
• The exhaust from coke-making (if manufactured rather than purchased);
and
• The exhaust from the HC1 absorption system.
Theoretically, the process can work using a variety of fuels—purchased
coke, coal, oil, or even natural gas—but we believe that the method described
in the patents, using oil as described above, is the preferred method. Thus,
we have chosen an example based on No. 6 fuel oil with a 1% sulfur content.
65
-------
TABLE IV-17
ALCOA CHLORIDE PROCESS COOLING TOWER SLOWDOWN WASTEWATER TREATMENT COSTS
(Basis: 160,000 Ton/Yr Aluminum Production)
CAPITAL INVESTMENT - S37S.OOO
VARIABLE COSTS
Operating Laboi
} man-hr/ Sll.38/man-hr
(incl di g suprvis
taint na ce
(Incl di g Labor +
Cheai al
• 5u fu Dioxide
• Line
• Sulfuric Acid
Fuel
Electrical Power
Sludge Disposal
* OHD) yr
OHD)
75 tun/yr
80 Con/yr
38 ton/yr
53,700 kUh/yr
750 ton/yr
$340/ct>n
$30.75/101.
$51. IS/ton
0.012/kUh
$5.00/ton
4.7 x 10~4
5.0 x 10~4
2.4 x 10~*
0.36
4.7 x 10~3
(( 107 solids)
TOTAL VARIABLE COST
FIXED COST
Taxes 6 Insurance
-------
TABLE IV-18
AND HC1 POLLUTION CONTROL COSTS FOR ALCOA CHLORIDE PROCESS
(Basis: 160,000-Ton/Yr Aluminum Production)
CAPITAL INVESTMENT (CI)
VARIABLE COSTS
Electric Power Purchased
Labor Wages
Supervisory Wages
Maintenance Labor, Super-
vision, Materials and
Supplies
Labor Overhead
Chemicals
• Lime
• Soda Asb
Residue Disposal
Total
riXED COSTS
Plant Overhead
Local Taxes and
Insurance
Depreciation
TOTAL PRODUCTION COSTS
Return on Investment
(pretax)
TOTAL (S/yr)
TOTAL ($ per ton aluminum)
Units Used
In Costing
or Annual
Cost Basis
kWh
man-hr
15!! labor
sz ci
32% wages
ton
ton
ton
60% wages
2% Cl
CI/14
20* CI
$/Unit
$6.50
30.75
56.00
5.00
S02
Control
$3,700,000
75,000
57,000
8,600
185,000
21,000
759,800
39,400
74,000
264,300
1,684,600
740,000
2,424,600
$15.15
HC1
Control
$155,000
1,200
1,000
150
7,750
370
57,400
67,870
690
3,100
11,000
2,660
31,000
113,660
$0.71
Every four years or so when the cells are relined, the old refractory
would have to be discarded. Similarly there would be miscellaneous minor
wastes from the aluminum casting operations; much of these latter wastes would,
in any case, be similar to those from the Hall process. The properties of
these solid wastes should permit disposal to approved chemical landfills.
Pollution Control Costs and Energy Use
Tables IV-14, IV-15 and IV-16 summarize pollution control costs and
^nergy use for the Alcoa process. The major user of energy for environ-
mental control is the scrubber for the S02 system. Both costs and energy use
for pollution control are estimated to be considerably less than the base line
Hall process where pollution control energy use amounts to less than 1% of
total process requirements.
(6) Process Energy Use
One of the chief advantages claimed for the chloride process relative to
the Hall process is its lower electrical requirement, about 5.2 kWh/lb of alu-
minum, delivered at a potential of 3.3 volts (U.S. Patent 3,725,222). For a
bath of about 5% A1C13 in 50% NaCl/LiCl, the reversible decomposition voltage
is about 1.95 volt (U.S. Patent 3,847,761). The current efficiency, using
12,158 "ampere-hours per Ib-equivalent as the value of the Faraday and remem-
bering that there are three equivalents per Ib mol (27 Ib) of aluminum, is
easily shown to be quite high:
67
-------
3 x 12,158
Current Efficiency = (5.2 x 1,000/3.3) (27) = 86%
Note that the chloride process figure of 5.2 kWh/lb aluminum compares
very favorably with the 7.8 and 6 kWh/lb aluminum needed for the present and
projected new Hall-Heroult cells respectively.
The fossil fuel requirement of about 25 x 10 Btu/ton of aluminum in the
chloride process is higher than that of the Hall process; when one considers
the fuel value of the coke, pitch, and natural gas in the Hall process, the
total fuel value of "fossil-based materials" is about the same for the two
processes. The Alcoa chloride process energy savings are largely due to the
smaller electrical power utilization.
(7) Economic Factors
It is difficult to estimate costs for .this process, for which details are
lacking. It has been suggested (Peacey and Davenport, July 1974) that a new
chloride plant ought to be somewhat cheaper than a new Hall plant. We believe
these authors have not adequately taken into account the complexity of the
chloride process, which counteracts the savings from elimination of the anode-
baking operation and from the smaller floor area for the multipolar cells. On
this basis, we have chosen to equate the capital investment for both processes
at $l,750/annual ton of aluminum (March 1975 basis).
An estimate of the operating cost for a new Alcoa chloride process plant
is shown in Table IV-19. Table IV-19 presents the cost of the operation
described above which we believe is the preferred method of operating this
process. As seen, the estimated cost for environmental control for the Alcoa
process is only a small fraction of the production costs.
(8) Technical Considerations
The degree of technical risk is not known, but Alcoa presumably would not
be building a 15,000-ton/yr demonstration smelter unless it were optimistic
about the process. There is a good body of information on reductive chlorina-
tion of ores and on separation of volatile metal chlorides; molten salt chloride
electrolysis is already commercial practice in the manufacture of magnesium
metal. For these reasons, we believe that the risk of technical failure is
not a major one for the Alcoa chloride process. There may, on the other hand,
be problems with impurity buildups in portions of the processing loop, or in
lower chlorination yields than expected, etc., which can affect the projected
costs. Such problems ought to be soluble, however, and the process appears
ultimately to offer some significant advantages over the Hall process.
b. Refractory Hard Metal Cathodes
(1) Background
The prospect of refractory hard metal cathodes for use in the aluminum
industry has been of interest for some 15-18 years. Early work on this subject
68
-------
TABLE IV-19
ESTIMATED PRODUCTION COSTS FOR NEW ALUMINUM PLANT, 1975
(Alcoa Chloride Process)
Product:
Aluminum
Annual Capacity: 160,000 tons
Process: Alcoa Chloride
Capital Investment: $280.000.000
Location: Kentucky-Tennessee
Annual Production: 160.000 tons
VARIABLE COSTS
Raw Materials
Bayer Alumina
Oxygen
Nad
LiCl
Chlorine
Byproduct Credits
• 35% HC1 Solution
Energy
• Purchased Fuel (No. 6
Fuel Oil)
• Electric Power Purchased
• Miscellaneous
Water
• Process
• Cooling
Direct Operating Labor (Wages)
Direct Supervisory Wages
Maintenance Labor (Wages)
Maintenance Supervision (Wages)
Maintenance Materials
Labor Overhead
Misc. Variable Costs/Credits
TOTAL VARIABLE COSTS
FIXED COST
Plant Overhead
Local Taxes and Insurance
Depreciation
TOTAL PRODUCTION COSTS
Return on Investment (pretax)
Pollution Control
TOTAL
Units Used in
Costing or
Annual Cost
Basis
ton
ton
ton
ton
ton
ton HCL
106 Btu
kWh
10 gal
103 gal
Man-hr
15% Op. Lbr.
Man-hr
15%. Mnt. Lbr.
2.5% CI
32% of wages
•
60% of wages
2% of CI
7.1% of CI
20% of CI
S/Unit
125.00
25.00
30.00
2000.00
105.00
27.00
2.00
0.012
(1.50
0.05
6.50
6.50
Units Consumed
per Net Ton
of Product
1.93
0.02
0.001
0.001
0.19
-0.19
24.85
10500.00
0.2
100.00
3.5
4". 5
$ per Net Ton
of Product
241.25
0.40
0.03
2.00
19.95
-5.08
49.70
126.00
0.10
5.00
22.75
3.41
29.25
4.38
43.75
19.13
562.02
35.87
35.00
124.25
757.14
350.00
16.50
1,123.64
69
-------
was carried out by Kaiser and British Aluminum. In the early days, several
different materials were considered as potential refractory hard metals for
use as cathodes in place of the graphite cathodes presently used in the Hall-
Heroult cells. The materials originally considered were zirconium and titanium
carbides and borides and some mixtures thereof.
Since then, carbides of both metals and zirconium boride have been elimi-
nated from consideration so that, at present, principal interest is in titanium
diboride because of its superior electrical conductivity, and the fact that
it is wetted by molten aluminum and cryolite in the cell. Also, in the pure
state it is not corroded by the electrolyte. Thus, there is hope that this
material, properly fabricated, would last for a minimum of four years. This
is the requirement for cathodes since the cell itself has a normal life of
four years, although some cell lives have been reported to last up to six years.
(2) Past Difficulties and Considerations
Originally, these materials were considered as a means of reducing the
voltage drop at the various interfaces in the cathode hardware. In the present
cathode arrangement used in the Hall cells, there are four connections, each
of which involves a certain amount of voltage drop. The first connection is
the one. between the bus bar and the iron cathode support—current distribution
b'ar; the second, between the iron and the carbon cathode; the third, between
the carbon cathode and the molten aluminum; and the fourth, between the molten
aluminum and the electrolyte. Of these, the most important, i.e., the one
having the highest voltage drop, occurs between the carbon and the molten alu-
minum metal pad which results partly from the formation of sludge and aluminum
carbide at this interface. Under the best conditions, the drop across this
interface is 0.4 volt, but it can be as high as 0.75 volt. The voltage drop
between the cathode bus to the surface of the carbon anode amounts to a total
of about 0.5 volt.
Originally, the thinking was to eliminate the voltage drop between the
iron and the carbon and to reduce the voltage drop between the cathode bus and
the aluminum pad by replacing the iron and carbon with titanium diboride. In
theory, it can be shown quite readily that the voltage drop incurred in passing
electric current through a conductor of optimum dimensions and with a normal
Lorenz function with respect to thermal and electrical conductivity when the
ends are maintained (as in aluminum cells) at 95°F and 1785°F is on the order
of 0.18-0.19 volt. This means that if an appropriate material, such as titanium
diboride, could be produced, the cathode voltage drop might be reduced to less
than half of the existing value.
This concept would remove the iron and carbon from the cathode system to
be replaced by titanium diboride, which is much more compatible with molten
aluminum than the carbon presently used, because high-resistance aluminum car-
bide forms at this interface. This, in turn, creates more heat in the cathode
as a source of power loss to heat rather than disassociation of aluminum oxide
in the electrolyte. However, by replacing the iron and carbon of the cathode
with titanium diboride, the savings in power would amount to only 5-10%.
70
-------
The important reason that nothing has been done with this concept in the
past is that there have been difficulties vith the stability of the titanium
diboride cathodes due to spalling, cracking, and, in general, short cathode
life in the cell. Part of these past difficulties may have been due to the
presence of titanium carbide as an impurity from the original manufacturing
process for producing titanium diboride. It is now well known that titanium
carbide makes the titanium diboride more sensitive to corrosion, stress crack-
ing, and thermal shock.
(3) Present Concepts and Activities
More recently, interest has shifted to replacing not only the iron and
the carbon, but also the molten aluminum pad so that the titanium diboride
would provide connections between the cathode bus and the electrolyte. There
is a much greater advantage in this arrangement because it implies that the
aluminum produced at the cathode could be rapidly removed or drained from the
cathode so that only a thin film of molten aluminum would ever exist on the
titanium diboride. This would significantly reduce the drop through the
molten aluminum. It has further advantages in the cell system. Because
there would be only a thin film of molten aluminum on the cathode, which would
reduce or largely eliminate the back reaction that occurs at the anode, alu-
minum reacting with CC>2 to form CO and aluminum oxide would be minimized and
the Faraday efficiency improved. In conventional Hall-Heroult cells, the high
current flux tends to create a so-called fog of aluminum particles between the
anode and cathode in the electrolyte, which provides opportunity for this back
reaction. With thin films of molten aluminum on the titanium diboride cath-
odes, there is little, if any, tendency to sweep molten aluminum from the
titanium diboride surface wetted by the molten aluminum. This would permit
closing the distance between the anode and cathode which, in turns, would
reduce the voltage drop through the electrolyte, and at the same time permit
an increase in anode current density. This in turn would mean more current
flow and more disassociation so that more aluminum would be produced.
It is anticipated by those working on this development in the industry
that a power saving of the order of 30-40% could be achieved during periods
of production curtailment, i.e., periods of low aluminum demand. In addition,
it is also believed that during periods of high demand, current flow could be
increased and, therefore, production would be increased. This would require
reducing the anode/cathode distance to reduce the voltage drop and avoid over-
heating the cell by the higher current flow. It is currently believed that
production increases with corresponding current flow increases .of 30-50% are
possible. It is unlikely that any power saving would result from a 50%
increase in current flow and 50% increase in production. However, it is con-
servatively believed that a 15-20% saving in power, along with a simultaneous
30% increase in production, is attainable. This contention is based upon
some current experience and expectation that satisfactory titanium diboride
cathodes can be made that will survive the atmosphere of the electrolyte in
the Hall-Heroult cells for four to five years. Apparently, at least two
companies, specifically Kawecki Berylco Industries, Inc. and PPG Industries,
feel that the past difficulties with titanium diboride have now been overcome,
and they believe that they could demonstrate long (3-4 years) cathode life
and the advantages of titanium diboride cathodes to the aluminum companies.
71
-------
In the past, and even now, the aluminum companies have looked to pro-
ducers of these refractory hard metals to provide materials that would operate
satisfactorily in the aluminum cells. The aluminum companies have been coop-
erative in terms of testing and analyzing the results, but have not undertaken
much internal research on the problem of providing the desired cathode
materials. The remaining problems seem to be a full demonstration of cathode
life, which must be at least four years, and hopefully, longer. Views differ
in the industry with respect to the present situation. Some believe that the
price of the fabricated materials is too high, which is the view of British
Aluminum, while others believe that the potential saving would support a very
high price for the new titanium boride cathodes.
(4) Costs of the Cathodes
It is difficult to obtain real costs or prices for titanium diboride
cathodes that will ultimately apply, because each of the aluminum producers
has different conceptual configurations which they consider to be proprietary.
Moreover, although these configurations are known to suppliers, they are priv-
ileged information which cannot be released. However, we understand that the
raw material cost is $15.50-$22.00/lb and that fabrication is presently 2.5
times that number, which means that a cubic inch of fabricated titanium
diboride would cost about $38.75. It must be recognized that at present
there is no large-scale production or fabrication of these materials and that
the cost would logically be much higher now than in the future. If this
development becomes a commercial reality in the aluminum industry, production
volume would increase and costs for fabricated cathodes might be one-half to
one-third of these present costs. Conventional carbon cathodes that last 3-4
years would cost $2-3 per ton of aluminum produced over the above life of
the cell.
There is no doubt that the cost of fabricated diboride would be much
higher than present carbon cathodes.' Therefore, the titanium diboride
cathode configurations must have a high surface-to-weight ratio. This proba-
bly means thin sections which may require supports. Among the aluminum pro-
ducers that are active in this field, there is a lot of work going on with
respect to titanium diboride cathode configurations and the support of such
thin sections, in the cell.
(5) Status of Development
There is at present an increased activity and excitement in the aluminum
industry and among producers of titanium diboride with respect to the poten-
tial of cathodes made from this material in the reduction cells. The problem
is to demonstrate life under active cell operations and, if a four-year life
is demonstrated, we believe that rapid implementation can be expected. The
incentives are so great that increased activity on this development is
expected. In view of the above, it is difficult -to set a time expectatio'n ori
implementation.
72
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(6) Effluent Control
As discussed in Appendix C, which deals with the pollution problems of the
existing Hall primary aluminum smelting process, the major sources of water
pollution are wastewater streams created by the use of wet air pollution con-
trol devices. Major pollutants of concern from existing aluminum smelting
operations are fluorides and suspended solids.
Although a number of the heavy metals present as impurities in the alu-
mina feed may ultimately find their way into wastewater streams, these usually
occur in such low concentrations as to make their removal either technically or
economically impracticable, a fact recognized in the establishment of guide-
lines for the 1973 and 1983 effluent limitations. Since the effluent limita-
tions are applied only to suspended solids, fluoride, and pH, it is important
to recognize what effects the retrofitting of present smelters with titanium
diboride cathode might have on the capabilities of presently installed pollu-
tion control equipment in meeting effluent limitation guidelines.
The existing Hall process uses cryolite and aluminum fluoride as fluxing
agents, thereby producing an off-gas consisting largely of equal parts of car-
bon dioxide and carbon monoxide, particulates in the form of insoluble fluor-
ides, hydrogen fluoride and fluorine. The effect of the use of titanium
diboride cathode in the Hall-Heroult cells would be as follows:
• The back reaction in which aluminum reacts with carbon dioxide to
produce alumina and carbon monoxide would be substantially reduced;
this would mean that the off-gas would contain less carbon monoxide
and more carbon dioxide. It would also mean that a slightly lower,
or the same, volume of carbonaceous gas would be released at the
anode, even assuming that the production rate would increase per
cell by 30%.
• Fluoride and particulate emissions are related to aluminum pro-
duction so that the concentration of fluorides in the off-gases
from the cell would increase by approximately 30% as a result of
the increased production possible.
Thus, as suggested by the estimated pollution control costs shown in
Table IV-14, we judge that the overall effect would be about the same volume
of off-gas per unit time with a 30% increase in the fluoride and particulate
content of the gas. Consequently, in a retrofit situation it is likely that
off-gas handling equipment would be generally adequate in most existing
smelters to handle the off-gases resulting from the installation of titanium
diboride cathodes. However, capacity would have to be checked in each
retrofit. On the other hand, the feed rate of any reagents, such as calcium
oxide or alumina used to eliminate fluorides—calcium fluoride, cryolite,
or aluminum fluoride—would have to be increased to take care of the increased
emissions of fluorides from the cells as a result of increased production.
The increases would be proportional to the increase in aluminum production
rate.
73
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Obviously, if the dry emission control process were installed on an
existing smelter, the effect, even on a fluoride recovery system, would be
minor because, while more fluoride would be emitted per unit time, more
alumina would be consumed and would be available for removing fluorides as
aluminum fluoride, which would go back as feed to the cell, i.e., the rates
would be proportional.
The net result is that we doubt that there would be any significant
effect on pollution control systems presently existing in aluminum smelters
as a result of retrofitting the installations with titanium diboride cathodes
in place of the graphite cathodes presently used. It should be understood
that in either case-'-carbon or titanium diboride—the cathode is inert, i.e.,
it does not enter into the reaction, only the anode carbon is consumed and,
of course, is the source of the carbon monoxide and carbon dioxide emitting
from the existing cells. The same would still be true after the installation
of titanium diboride cathodes.
With regard to the solid waste problem inherent in the disposal of old
refractory linings removed before rebuilding cells, this problem would also
remain unchanged if we assume the same cell life. This would have to be the
case, because the titanium diboride cathode would not be installed if its use
significantly reduced cell life. The value of the titanium diboride scrap
cathode is high enough to recover the material for return to the cathode
manufacturers.
(7) Energy Use
If the back reaction, which presently occurs in the anode of the conven-
tional Hall-Heroult cell operation, is largely eliminated, as might be
expected with the use of titanium diboride cathodes, then there would be a
reduction in the consumption of anode carbon - and therefore, petroleum coke.
and pitch - of about 20%. This means there would be a reduction in purchased
fuel from 24 x 10° Btu consumed per ton of aluminum by the present smelters
to about 20 x 10^ Btu/ton of aluminum when titanium diboride cathodes were
used. Power consumption would be reduced from 15,600 kWh/ton in existing
smelters to 12,480 kWh/ton of aluminum. Converted to a fossil fuel equivalent
basis, i.e., considering the inefficiencies in power generation, the total
energy consumption amounts to 151.2 x 10^ Btu with the use of titanium dibor-
ide cathodes. This compares favorably with the total energy consumption in
the existing smelting process using carbon cathodes, which is 187.8 x 10°
Btu/ton of aluminum. As with the base line Hall process, pollution control
energy use is less than 1% of process energy requirements. Thus an overall
energy saving of 19% is potentially achievable by conversion to titanium
diboride cathodes.
(8) Economic Factors
It is difficult to anticipate how the industry will take advantage of •=
this development. We have assumed it will retrofit its existing large cells
to take advantage of the potential of increasing production, while at the
same time reducing energy consumption by 20%, as appears possible with the
74
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use of titanium diboride cathodes. This approach would permit retiring some
of the older, less efficient pot lines that have relatively small cells by
today's standards. Of course, the major consideration is electrical power
so that it is unlikely the industry would retire cell lines in areas where
there is a continued potential for low-cost power. Nevertheless, we doubt
that they would use the total potential for energy savings, except in periods
of production curtailment. In Table IV-20 we have presented our estimates of
the costs resulting from the application of titanium diboride cathodes in an
existing carbon cathode smelter of 160,000-ton/yr nominal capacity; such a
change would increase smelter output by 30% to an estimated 208,000-ton/yr
and would have further cost consequences as discussed below.
If the back reaction could be entirely eliminated at the anode, the anode
consumption could be reduced by 25%. However, we have assumed that the back
reaction would be largely, but not entirely, eliminated, so that calcined coke
and pitch consumption would be reduced by only 20%.
As mentioned above, we also assumed that the power consumption would be
reduced by 20%, while the cell lines would be producing approximately 30%
more metal. There would be a slight reduction in operating labor and operat-
ing labor supervision, but no reduction in maintenance labor and maintenance
supervision. We have included an estimated cost for titanium diboride cath-
odes. This is actually an amortization factor assuming a four-year cathode
life at a cost of $12.90/cu in.
This calculation is based on several assumptions. First, we assumed that
the costs of titanium diboride cathodes, fully fabricated, would be reduced to
one-third of present costs, based upon the assumption that, with large-scale
production and fabrication of cathodes, costs would be reduced to this extent,
and that costs would be substantial but affordable, as one of the men working
in the field said. We also assumed that the cathodes would be fabricated in
tiles or sheets 3/16 in. in thickness supported by suitable refractory or
carbon blocks. This is based on our understanding that the fabrication would
be in relatively thin sections with a high surface-to-weight or -volume ratio
to minimize the cost of titanium diboride cathodes per unit area. We further
assumed that the current density would be increased by about 30% of that
presently used in carbon cathodes.
The costs presented in Table IV-20 for an older aluminum smelter with
a nominal capacity of 160,000-ton/yr producing 208,000-ton/yr with titanium
diboride cells would typically have an undepreciated investment of about $140
million. This is about average for the present existing aluminum industry,
based on information obtained from major financing sources. This basis includes
the additional investment would have to be made, amounting to $42 million, to
provide some increase in capacity for handling the increased production of
aluminum, increased storage and handling for alumina, cryolite, aluminum flu-
oride, and increased capacity for pollution control.
. An existing plant retrofitted with titanium diboride cathodes would pro-
duce aluminum at $733/ton. This is about the same as for a plant operating
conventionally with carbon cathodes, which w.ould produce aluminum at a cost
of $742-/ton. Although this seems like a minor reduction, it becomes a much
75
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TABLE IV-20
ESTIMATED PRODUCTION COSTS IN EXISTING ALUMINUM PLANT WITH
TITANIUM DIBORIDE CATHODES, 1975
Product: Aluminum
Process: Hall with Titanium Diboride Location: Kentucky-Tennessee
Cathodes
Annual Capacity: 208,000 Net Tons Fixed Investment:
Annual Production: 206,000 Net Tons
VARIABLE COSTS
Raw Materials
• Bayer Alumina
• Cryolite ,
• Aluminum Fluoride
Energy
• Purchased Fuel
Natural Gas
• Calcined Coke
• Pitch
• Electric Power Purchased
• Miscellaneous
Water
• Process
• Cooling
Direct Operating Labor (Wages)
Direct Supervisory Wages
Maintenance Labor (Wages)
Maintenance Supervision (Wages)
Maintenance Materials
Labor Overhead
Misc. Variable Costs/Credits
• Cost Titanium Diboride
Cathodes
TOTAL VARIABLE COSTS
FIXED COSTS
Plant Overhead
Local Taxes and 'Insurance
Depreciation
TOTAL PRODUCTION COSTS
Return on Investment (pretax)
Pollution Control
TOTAL
Undepreciated Investment (U.I.) $140,
1975 Replacement Costs $280,000,000 -j
New Investment for Retrofitting (R.C.
Units Used in
Costing or
Annual Cost
Basis
net ton
net ton
net ton
106 Btu
net ton
net ton
kWh
Man-hr
15% of Op. Lbr.
Man-hr
15% of Mnt. Lbr.
2.555 of RC
327. of wages
Est.
60% of wages
2Z of UI
7.1Z of UI
5% of UI
000,000
) $42,000,000
$/Unit
125.00
336.00
350.00
1.50
80.00
70.60
0.01
6.50
6.50
Units Consumed
• per Net Ton
of Product
1.93
0.035
0.020
6.1
0.42
0.12
12,480.00
2.5
4.5
$ per Net Ton
of Product
241.25
11.76
7.00
9.90
33.60
8.47
124.80
16.25
2.44
29.25
4.39
38.70
16.74
25.73
569.55
31.39
13.46
47.79
662.19
33.65
37.20
733.04
76
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more important saving, if one considers the capital and operating cost of
new aluminum capacity. The cost of new aluminum capacity at $1750/annual
ton for the 48,000 tons of increased output from this plant would involve
a capital expenditure of $84 million and the production cost of aluminum
from a new smelter including return on investment, would be $1181/ton.
(9) .Technical Considerations
The degree of technical risk is minimal. The cathode life is the big
risk so that cathode life and performance will have to be demonstrated on a
number of commercial cells before large numbers of pots are retrofitted. This
will take some time, but the development could be very important and dramatic
to the aluminum industry.
(10) Effect on Intermediate and Final Products
There would be no anticipated effect on the intermediate or final prod-
ucts - cast sows semifinished or finished forms.
c. Toth Aluminum Process
Dr. Charles Toth, Board Chairman of Toth Aluminum Corporation (TAG), has
proposed a pyrometallurgical process for the production of aluminum as a pro-
posed competitor to the Hall-Heroult electrolytic reduction process. The
basis of the process is the reduction of aluminum chloride with manganese
metal, forming manganese chloride and aluminum. The sequence of chemical or
pyrometallurgical reactions involved in the process is presented below:
Toth Aluminum
Reaction Sequence
Feed Feed
i +
(T) 3C12 + 1-k + A1203 -v 2A1C13 +
, 1
3Mn + 2A1C13 •*• 3MhCl2 + 2A1 -> Product
J/
3C12 + UMi203 * 3MnCl2 +
3Mn + 4^CO •*• 4|C + l|Mn203
Feed
77
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This is an interesting reduction sequence in which the net overall reac-
tion is A1203 + 7.5C + 2.2502—«~2A1 + 7.SCO. Recently Toth informed his
stockholders that the firm had experienced difficulty in carrying out Reaction
2, i.e., the reduction of aluminum chloride with manganese to form manganese
chloride and aluminum metal. They have found that it was difficult to com-
pletely utilize the manganese metal and that the resulting aluminum product
was contaminated with manganese metal. They indicated that the reaction
would go to the extent that 80% of the manganese metal is consumed, but that
20% remains unreacted and thus represents a contamination of the aluminum
product. Since, at the present time, TAG is no longer offering this process
until more research is completed, no detailed consideration was given to this
process in this study. The descriptive material on the Toth aluminum process
that follows is included for those interested in the conceptual details of
the process.
(1) Chlorination of Alumina
Reaction (1) involves the chlorination of alumina in the presence of
carbon_to form aluminum trichloride, carbon monoxide and carbon dioxide.
This step in the process has been operated commercially at l650°F in a fluid-
ized bed reactor with an alumina feed. Any sodium present would also be
chlorinated and would be volatilized, as indicated in recent Alcoa patents,
forming a mixed NaCl-AlClg salt soluble in A1C13. Since the sodium present
in Bayer alumina is small, the formation of the double salt is not considered
a serious problem.
We anticipate that the alumina feed would be preheated, but that the
reaction would be at least slightly exothermic even if the reaction took
place in the presence of excess carbon so that the off-gases were largely
carbon monoxide.
The aluminum trichloride, of course, volatilizes and can be recovered by
condensation at about 200°F.
(2) Reduction of Aluminum Chloride with Metallic Manganese
The next step in the sequence is the reaction between aluminum trichlor-
ide and manganese metal to form manganese chloride and product aluminum
metal. This reaction would probably be carried out in liquid aluminum chlor-
ide at about 575-°F and 200 psig. It is believed that an excess of aluminum
chloride would be required to completely utilize the manganese, if possible.
Particles of metallic aluminum produced by this reaction would be separated
from the manganese chloride and excess aluminum chloride by some means as yet
unspecified.
(3) Oxidation of Manganese Chloride to Manganese Oxide and Chlorine
for Recycle
The next step in the process is Reaction (3) in which manganese chloride
is oxidized to manganese sesquioxide with liberation of chlorine for recycle.
This could be carried out in a fluid-bed reactor operating at 1100°F in which
solid manganese chloride is contacted with oxygen. Gaseous chlorine and solid
e the reaction products.
78
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(4) Reduction of Manganese Oxide to Manganese Metal for Recycle
The final step in the operation is the reduction of manganese ••aeuloxie'e
with carbon back to manganese metal, which of course is recycled to leactiem
(2). Originally, it was proposed to carry out this reduction in a blast fur-
nace in which the manganese sesquioxide would be reduced to manganous oxide
(MnO) by heat, or carbon monoxide, with the resulting manganous oxide reduced
by coke to the metal with the evolution of CO. The procedure ha* since
appeared to be difficult, and it is now anticipated that the reduction of the
manganese sesquioxide would more logically be carried out in a. submerjed arc
electric reduction furnace to produce molten manganese metal vhich vewld be
cooled and recirculated to the aluminum generator.
d. Combination of the Clay Chlbrination Process and the Alcoa
Chloride Process
(1) Basis of Analysis
An interesting combination is one involving aluminum chloride produced
from clay via a clay chlorination process concept as direct aluminum chloride
feed to new Alcoa chloride electrolysis cells for production of aluminum.
As an example of a clay chlorination process, we used the .Toth algmina
process. In this analysis we sized the Toth process installation for clay
chlorination to produce sufficient aluminum chloride feed to the Alcoa chlor-
ide electrolytic cells to produce 160,000 ton/yr of primary aluminun. Thi«
means the Toth clay chlorination installation would be sized at a capacity of
44% of the 700,000 ton/yr plant discussed earlier. Toth alumina from the
clay process was discussed earlier in this chapter for production of alumina
for consumption in conventional Hall-Heroult aluminum smelters. This smaller
capacity installation of the Toth process to match a nominal size aluminum
smelter requirement for aluminum feed represents a cost penalty, since there
is an economic benefit to large-scale recovery of alumina from aluninum-
bearing raw materials. This is supported by the fact that new Bayer process
installations are much larger in terms of production capacity than the typical
older Bayer process plants presently operating in the United States.
(2) The Combined Process Operations
In this combination, the Toth clay chlorination process originally con-
ceived for production of alumina from clay replaces the aluminum chloride
feed preparation part of the Alcoa chloride process in which pot feed alumina
is chlorinated in the presence ,of carbon to yield the aluminum chloride feed
to the Alcoa chloride cells.
The operation of the feed preparation part of this combination preeess
differs slightly from that of the Toth alumina process described earlier in
the fallowing respects.
Since aluminum chloride is required instead of alumina as feed to the
cells, the reoxidation of aluminum chloride is eliminated from the operation
which reduces the oxygen requirements significantly. The feed to the cells
79
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comes directly from the final distillation separation of ferric chloride
from the aluminum chloride, as described in detail previously in this chapter
of the report.
The operation of the cell feed preparation section of this combination
process differs very significantly from the cell feed preparation section of
the Alcoa chloride process described in detail earlier. Instead of pot feed
alumina, the starting raw material is clay. Instead of a heavy oil coked on
the alumina particles, the reductant is coke. Because of the larger volume
of impurities in the clay, as compared with the high-purity alumina feed, the
feed preparation is more complicated, requires more separation steps, and pro-
duces a byproduct titanium dioxide. The feed preparation section of this com-
bination process involves all the steps of the Toth alumina-from-clay process
up to the final oxidation of the aluminum chloride to alumina.
(3) Effluent Control
This combination process has all of the effluent control problems of the
Toth alumina process, plus some of the effluent control problems of the Alcoa
process, viz., those originating from the chloride cell operation. Details
on these problems and their costs are found in the sections of this report
dealing with the Toth and Alcoa processes.
(4) Energy Use
This combination process consumes 10,637 kWh per ton of aluminum which
is much lower than the electric power consumption of 15,600 kWh per ton of
aluminum used in existing Hall-Heroult smelters, but higher than the 10,500
kWh per ton of aluminum required in the Alcoa chloride process. This combi-
nation process requires coal and coke amounting to 48.5 x 10^ Btu per ton of
aluminum which is significantly higher than the purchased feed for a new
Bayer-Hall-Heroult process of 38.6 x 106 Btu/ton.
The total energy consumed by this combination process converted to a
fossil fuel basis, i.e., considering the inefficiencies of power generation,
would amount to 160 x 10^ Btu/ton of aluminum. This compares favorably with
the existing Hall-Heroult process that consumes 188 x 10° Btu/ton. However,
if one includes the energy for the production of alumina to make the analysis
comparable, the total energy of the combination new Bayer-Hall-Heroult pro-
cess would amount to 164.6 x 10^ Btu/ton of aluminum, which is a little higher
than the Toth-Alcoa combination estimated at 160 x 10^ Btu/ton of aluminum.
(5) Economic Factors
In Table IV-21 we have presented our estimates of the operating costs
for this combination process for the production of aluminum at capacity of
160,000-ton/yr. Based upon the estimates summarized in Table IV-13, the
costs look attractive. The capital cost estimate is based on the cost of
the Toth alumina-from-clay process, less the alumina chloride oxidation,
scaled to the size needed to supply the Alcoa chloride cells with enough
aluminum chloride to produce 160,000-ton/yr of primary aluminum metal.
80
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TABLE IV-21
ESTIMATED PRODUCTION COSTS FOR NEW ALUMINUM PLANT, 1975
(Combination of Toth Alumina and Alcoa Chloride Aluminum Processes)
Product:
Aluminum
Annual Capacity: 160,000 tons
Process: loth-Alcoa AlClj Electrolysis Location: Georgia
Capital Investment (CI): $296,000,000 Annual Production: 160,000 tons
VARIABLE COSTS
Raw Materials
Clay (Kaolin)
Chlorine
Oxygen
NaCl
LiCl
Byproduct Credits (Crude Ti02)
Energy
• Purchased Fuel
Coal
Coke
• Electric Power Purchased
Water
• Process
• Cooling
Direct Operating Labor (Wages)
Direct Supervisory Wages
Maintenance Labor (Wages)
Maintenance Supervision (Wages)
Maintenance Materials
Labor Overhead
Misc. Variable Costs/Credits
• Other Operating Supplies
TOTAL VARIABLE COSTS
FIXED COSTS
Plant Overhead
Local Taxes and Insurance
Depreciation
TOTAL PRODUCTION COSTS
Return on Investment (Pretax)
Pollution Control
TOTAL
Units Used in
Costing or
Annual Cost
Basis
ton
ton
ton
ton
ton
ton
106 Btu
ton
kWh
103 gal
103 gal
Man-hr
152 Op. Lbr.
Man-hr
15% Mnt. Lbr.
2.5% of CI
32% of wages
60% of wages
2% of CI
7.1% of CI
20% of CI
$/Unit
2.50
125.00
12.00
30.00
2,000.00
332.00
0.82
35.00
0.015
0.50
0.05
6.50
6.75
Units Consumed
per Net Ton
of Product
5.79
0.08
1.62
0.001
0.001
0.11
16.31
1.24
10,637.00
1.54
140.00
5.56
7.62
5 per Net Ton
of Product
14.48
9.65
19.43
0.03
2.00
-37.16
13.37
42.23
159.55
0.77
7.00
36.11
5.42
51.43
7.71
46.25
32.21
11.00
11.39
432.87
60.39
37.00
131.35
661.61
370.00
37.35
1,068.96
81
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We estimated the cost of the chloride cell installation based upon recent
experience with the conventional magnesium cells in which magnesium is pro-
duced by electrolysis of magnesium chloride to molten magnesium and byproduct
chlorine for recycle, as would be the case with the Alcoa chloride process
cells. These estimates are speculative; neither the Toth alumina-from-clay
process nor the Alcoa chloride aluminum process has yet been built or operated
on a commercial scale. Moreover, the details of both of these processes are
very limited, so that the accuracy of the estimates is speculative. However,
based on these estimates, it would appear that the operating costs would be
higher, $l,069/ton of aluminum, than from an existing Bayer-Hall-Heroult oper-
ation ($742/ton) or for an existing Hall-Heroult smelter modified with titan-
ium diboride cathodes ($733/ton). However, the costs are estimated to be
lower than for a new conventional Hall-Heroult smelter which would produce
aluminum at an estimated $l,181/ton of aluminum, including return on invest-
ments, or a new Alcoa chloride process starting with Bayer alumina, ($11237
ton aluminum) when starting with bauxite at $125.00/ton. Bauxite produced in
a new facility is estimated to cost significantly more and further improves
the relative potential economics of clay chlorination with the Alcoa process.
(6) Status of the Process
This combination process has ho formal status, although we have heard
that Alcoa has talked with TAG, but we have no information on any arrangement
or understanding. The technology of the Toth alumina process, the cell feed
preparation section of this combination process, is complicated; much more
complicated than the cell feed preparation section of the Alcoa chloride
process with its starting raw material, high-purity Bayer alumina. It would
appear that Alcoa would prefer to start with a simpler process, starting with
high-purity alumina.
4. Summary of Production Costs and Energy Requirements for
Production of Aluminum
Table II-3 summarizes the costs and the energy consumption (on a fossil
fuel equivalent basis) for producing aluminum in the existing and new Hall-
Heroult electrolytic smelting plants and by the alternative Alcoa process. Costs
for the new Alcoa process must be compared with new Hall-Heroult smelters,
because it is obvious that no new plant could hope to compete with existing
plants. On the other hand, since the refractory hard metal cathodes could be
retrofitted in existing Hall-Heroult smelters, cost comparisons for this
option should be made with both existing and new plants.
While the costs of pollution control are not significant in the cost of
producing alumina, as discussed earlier, they are significant, almost 4%, in
the cost of producing aluminum from a new facility and 6% in an existing
plant. The Alcoa plant has the potential for reducing pollution control costs
since the use of fluoride compounds is eliminated.
82
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V. IMPLICATIONS OF POTENTIAL PROCESS CHANGES
IN THE ALUMINA/ALUMINUM INDUSTRY
A. PRODUCTION OF ALUMINA BY ACID LEACHING OF KAOLIN CLAYS
1. Impact on Pollution Control
a. Nitric Acid and Hydrochloric Acid Clay Leaching Processes
The application of either of these two processes would present an impact
on the environment as a result of producing solid and liquid wastes containing
soluble nitrates or chlorides. The solid wastes largely result from the separ-
ation of insoluble materials from the leaching step discharged from counter-
current washing thickeners at the final thickener underflow. This underflow
then goes through a filtration step in which the final water washing of the
insoluble solid waste occurs. Although this material has been rather carefully
washed before discharge, it could still contain some soluble nitrates or chlor-
ides, depending on the process.
In addition to this major discharge, in both processes there is a crystal-
lization step which removes impurities as nitrates or chlorides. To remove
these materials from the evaporator crystallizer circuit, a bleed stream must
be taken off to maintain the purity of the product alumina. In both processes
this bleed stream containing aluminum nitrate or chloride and impurities as
nitrates or chlorides is finally treated by decomposition to recover the ni-
trate or hydrogen chloride value. While aluminum chloride or aluminum nitrate
and some of the impurities, such as nitrates or chlorides, are decomposable,
chlorides of alkali and alkali earth metals would not be decomposed and nitrates
of the alkali metals decompose to nitrites. Nitrates are suspected of being
carcinogenic. The nitrates of the alkali earth metals are difficult to decompose
completely. Thus, there are likely to be soluble nitrates or chlorides in the
solid discharge from these decomposition steps.
Also, it is likely that there will be small gaseous emissions of unrecov-
ered oxides of nitrogen and hydrogen chloride from the acid recovery systems
which may have to be removed from_the off-gases in small scrubbers using alkali
solutions. These result in aqueous solutions of soluble nitrates or soluble
chlorides requiring discharge.
The cost of air pollution control will depend on specific location and
local regulations. The general location of these clay-based processes logically
would be on or along the kaolin belt in the State of Georgia which is an area
of high rainfall and high groundwater levels. Since the major pollution control
costs will be for methods to prevent leaching of soluble chlorides and nitrates,
and since there is no apparent economic value in the leached residues if zero
discharge is required, the best solution to the control problem would be to
discharge to a disposal tailing pond or dump lined with an impervious membrane.
This would represent the maximum costs.
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b. Clay Chlorinatlon
In the case of clay chlorination, such as the Toth alumina process, which
recovers alumina by chlorination of clay in the presence of carbon, we consid-
ered the possible pollution problems that could result from this process.
This is a dry process, i.e., there is no leaching involved; the aluminum
chloride is volatilized overhead, along with other chlorides, such as ferric
chloride, silicon tetrachloride, titanium tetrachloride, and even some of the
sodium present in the clay as sodium chloride. These chlorides are separated
by a combination of fractional condensation and distillation to produce separa-
ted fractions of aluminum chloride, silicon tetrachloride, and titanium tetra-
chloride, all of which are oxidized to recover chlorine for recycle to chlorin-
ation and the respective product oxides—primarily alumina product and byproduct
titanium dioxide—for sale.
There are several solid waste streams from these operations. The primary
stream is the bottom discharge of unreacted materials from the chlorination
step, i.e., the waste from the clay, which would be primarily silica, but is
likely to contain some soluble chlorides as well. This would be a dry material
unless slurried for disposal.
A second source of waste results from the separation of aluminum chloride
from ferric chloride and sodium chloride. To remove sodium and iron that would
build up in the separation system, a bleed stream containing ferric chloride,
sodium chloride, and some aluminum chloride would be taken off. This stream
would be oxidized to recover chlorine "before final discharge, but the final
discharged product would be iron oxide and alumina plus sodium chloride, and
possibly other soluble chlorides as a result of incomplete oxidation during
chlorine recovery.
A third source of waste would result from the oxidation of the separated
silicon tetrachloride to silica. TAG anticipates that some of this silica
might be sold, but most is likely to be waste which could contain soluble
chlorides and fine particulates that are likely to be slow to settle.
TAG proposes that the titanium tetrachloride be fully recovered and oxidized
to obtain chlorine for recycle and a crude titanium dioxide for sale so that this
would not be' a waste stream. We believe that complete sale of titanium dioxide
is possible because there is a market in the United States, even for a crude
titanium dioxide for reprocessing to pigment.
In addition to the above solid wastes, there would be liquid wastes from
scrubbing off-gases. The major possible source of gaseous emissions is the
off-gas from chlorination after final low-temperature condensation of the sili-
con and titanium tetrachlorides. The final tail gas would contain carbon monox-
ide and dioxide, some hydrogen chloride, and possibly some uncondensed silicon
tetrachloride which would hydrolyze. These undesirable gaseous emissions could
be removed by caustic or lime water scrubbing which would result in carbonates
and soluble chloride salts.
We have very little detailed information on these waste streams. The cost
of environmental control would depend on site location and local regulations.
However, if zero discharge is required, we believe again that the best solution
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would be 60 discharge to a disposal tailing pond or dump lined with an imper-
vious membrane. This would represent the best available technology. Of
course, other, more esoteric treatments might be necessary in certain locations,
but these might make the process totally uneconomical.
c. Summary of Pollution Control Costs
We estimate the maximum cost for pollution control, i.e., for zero dis-
charge, for the clay-based processes compared with the Bayer bauxite-based
processes to be as follows:
POLLUTION CONTROL COSTS PER NET TON OF ALUMINA
Bayer Hydrochloric Acid Nitric Acid Toth Chlorination
$1.40 $5.00 $19.00 $10.80
2. Energy Requirements
A comparison of energy requirements for the present Bayer alumina process
and the nitric acid, hydrochloric acid, and Toth chlorination processes for the
production of alumina are presented below:
Process
Power - kWh/ton
Fuel - 106 Btu/ton
Total - Fossil fuel
basis (106
Btu/ton)
Pollution Control
(106 Btu/ton)
Bayer
Alumina
Bauxite
275
11.64
14.53
0.05
ENERGY CONSUMPTION
10 Btu per Net Ton Alumina
Hydrochloric
Acid Leaching
Clay
134
37.8
39.2
0.02
Nitric Acid Toth
Leaching Chlorination
Clay Clay
139
25.3
26.8
0.7
333
25.09
28.6
0.3
Thus, it can be seen that the clay-based processes, if implemented, would
have an important upward impact on energy consumption, as compared with the
Bayer process which is the present technology. However, other political and
technical advantages will contribute to the decision.
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3. Factors Affecting the Possibility of Change
The major factor that would affect the possibility of change in clay
processing to produce alumina is the degree of concern that the U.S. aluminum
industry has with respect to the major dependence on foreign sources of
aluminum-containing raw materials. Also the concern that the government might
have with the resulting effect on foreign exchange is a factor.
As prices of foreign bauxite and alumina increase, foreign exchange
requirements would increase and interest in clay as a source of alumina would
also increase. The development of domestic clays would be enhanced if the
depletion allowance on clay were increased.
B. PRODUCTION OF ALUMINUM BY THE NEW ALCOA PROCESS AND BY THE RETROFITTING
OF TITANIUM DIBORIDE CATHODES TO THE CELLS
1. Impact on Pollution Control
a. Alcoa Process
The new Alcoa process presents different pollution problems as compared to
those of the present Hall-Heroult aluminum smelting process. First, with res-
pect to the molten salt electrolysis cells, the chloride cells would be fully
covered to avoid loss of chlorine from the anode which is recycled to the
chlorination step. It is likely that the cells would be operated under slight
positive pressure to avoid in-leakage of air or moisture._0xygen in any form is
undesirable in the cells and results in the formation of oxides that drop out
on the molten aluminum cathode as sludge that reduces the efficiency of the
cathode. As a result, it is possible that a small amount of chlorine may leak
out of the cell hoods at points where aluminum chloride is charged, but the
incentive is there to avoid losses of chlorine. However, with proper hooding,
the volume of gas -to be handled from the cell room would be less than from the
open Hall-Herout cells.
The system is quite different from the present Hall-Heroult cells where
crust-breaking is required and fluoride emissions occur. The Alcoa cells are
more like magnesium cells in which no crust-breaking is required and where
chlorine is removed at the anode. Carbon cathodes are also used, but are
inert, which means that no significant amount of carbon oxide gases is released
at the anode from the Alcoa cells.
The major air pollution source would be from the coker and chlorinator
off-gases. The coker in which fuel oil is cracked on the hot alumina Would
result in an off-gas containing some cracked .hydrocarbon gases and hydrogen
sulfide. Since these gases are subsequently burned to provide heat for
coking, the off-gas would have to be provided with facilities for SO control.
The off-gas from the chlorinator in which volatile aluminum chloride is
produced from alumina and coke would also contain carbon monoxide and carbon
dioxide. This gas would be subjected first to high-temperature condensation
to remove sodium chloride and unreacted alumina, but also some aluminum
chloride. This high-temperature condensate would be oxidized to recover
86
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chlorine for recycle and would produce a solid waste of alumina and sodium
chloride; the sodium chloride would be removed by leaching to yield alumina
for recycle to the chlorinator. This treatment would result in a waste aqueous
stream of sodium chloride.
The remaining gas, containing most of the aluminum chloride, would then
be subjected to low-temperature condensation to remove the aluminum chloride
as solids that would be charged to the cells. The remaining non-condensable
gases would consist largely of carbon monoxide, carbon dioxide, hydrogen
chloride, and possibly also some chlorinated hydrocarbons. The hydrogen
chloride results from moisture present in the chlorinator feed that would be
converted in the presence of carbon and chlorine. It would be removed from the
off-gas to produce byproduct hyrdochloric acid. After scrubbing with sodium
hydroxide to remove any remaining hydrogen chloride, the end-gas would be
incinerated by burning the remaining combustible gas, primarily carbon monox-
ide, in a combustion chamber.
The major pollution control costs would be to reduce gaseous emissions
i.e., hydrogen sulfide or S02, depending on whether the sulfur removal was
before or after burning the off-gas from the coker control and hydrogen chloride
emissions from the chlorinator off-gas.
The latter control, i.e., hydrogen chloride, would result in a liquid
waste stream containing sodium chloride. In addition, there would be a sodium
chloride-containing aqueous waste stream for the discharge of sodium contained
in the alumina. There would also be salts and sludges removed from the cells
to remove impurities periodically. It is likely that if these discharges con-
tain much lithium chloride, they would be treated to recover this expensive
salt for reuse and would result in an additional sodium chloride waste stream.
Considering the above, we estimate that the cost of pollution control
would amount to $12.44/ton of aluminum produced. If the sodium chloride stream
would have to be totally impounded, the costs would be $0.50 to $1.00/ton as a
result of installing a tailing pond lined with an impervious barrier. This
would depend on the specific location and local regulations.
b. Application of Titanium Diboride Cathodes to Existing Hall-Heroult Cells
These cathode materials, applied in existing plants, would not change the
pollution problems significantly; if anything, they might slightly reduce the
problem for the following reasons.
The consumption of, and therefore the production of, anode carbon would
be slightly less and thus the pollution, as a result of making anodes, would
be less. The volume of off-gas per ton of aluminum would be less from the anode
production and baking. The volume of off-gas from the cells would also be less
per ton of aluminum, but the concentration of fluoride in the off-gas would be
higher. However, the fluorides leaving the cell should remain about the same
per ton of aluminum produced.
All of the above effects result from reducing the back reaction of the
anode so that the off-gas from the anode would be largely carbon dioxide and
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less carbon monoxide. Since carbon dioxide takes more oxygen from the alumina
than is the case with carbon•monoxide, there is less carbon consumed, and the
volume of cell off-gas is less per ton of aluminum. However, if the cells were
to be operated to produce 30% more aluminum as expected, the gas. flow of the
cells would be about the same as before without the installation of the cathodes.
The cost of off-gas handling would be reduced. The cost of reagents to remove
the fluorides would remain the same per ton of aluminum produced.
The net result is that we would expect existing air pollution control sys-
tems in present smelters to be adequate to handle the effects of the installa-
tion of titanium diboride cathodes in existing plants and that the cost of
control would be no higher and, if anything, slightly lower than in the present
Hall-Heroult smelters per ton of aluminum, as detailed in Appendix C. Pollution
problems created by the manufacture of the diboride electrodes have not been
considered because there is no information on the process used to produce the
titanium diboride cathodes.
c. Summary of Anticipated Control Costs
We estimate pollution control investment and operating costs for the new
Alcoa process and the application of titanium diboride cathodes on the existing
aluminum smelters would be as shown in Tables IV—14 and IV-15.
In addition, it should be recognized that if power consumption per ton
of aluminum can be reduced by 20-30%, there are additional favorable effects on
the pollution problems. If power consumption is reduced, the production of power
is less, which means less fly ash and less SO. per ton of aluminum. This also
means less coal mined and a reduction of the magnitude of the environmental
problems relating to coal mining, all in proportion to the reduction.
2. Energy Requirements
A comparison of energy requirements for the present Hall-Heroult process
and the Alcoa chloride process and the application of titanium diboride cathodes
to existing cells is presented below:
ENERGY CONSUMPTION
10 Btu/Net Ton Aluminum
Existing
Existing Alcoa Hall-Heroult
Hall-Heroult Chloride Smelters
Smelters Process TiB2 Cathodes
Power - kWh/ton 15,600 10,500 12,480
Fuel - 106 Btu/ton 24.02 24.85 20.14
Total Fossil Fuel Basis
106 Btu 187.82 135.10 151.18
Pollution Control 106 Btu/ton 1.71 0.42 1.31
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It is obvious from the above that the incentive is to reduce energy consump-
tion, and the concomitant effect would be to reduce pollution problems and costs.
3. Factors Affecting the Possibility of Change
The incentive for the reduction in power consumption is enough to favor-
ably affect the chances of change in the reduction of alumina to aluminum in the
U.S. industry. The incentive will be increased as power costs increase, without
any additional pressure or effects that Federal agencies of the Government could
bring to bear on the situation. Thus, we believe that the potential for change
to these lower energy-consuming alternatives for the production of aluminum will
depend entirely upon the results of the research and the capital costs involved
in making the necessary changes.
C. AREAS OF RESEARCH
Probably the most promising area of research that would have the greatest
immediate effect on energy consumption and environmental problems would be the
introduction of titanium diboride cathodes in the existing plants. The research
and development work that is most important relates to the quality of the tita-
nium diboride cathodes. This is a materials problem that might justify some
Government-sponsored research or some funding to expand present research. The
materials research that is being carried out relating to this problem is largely
being done by the private sector, companies that are interested in titanium
diboride cathodes. These would include Kawecki Berylco Industries, Inc., PPG
Industries, Inc., and, in the past, Carborundum, Union Carbide Corporation,
and Norton. The present leaders in this field appear to be PPG and Kawecki
Berylco. The research that has been done is largely related to preparing and
testing materials in aluminum cells. It is more trial and error and adjustment
research, with the real problem that of demonstrating extended cathode life.
The payoff here would be large in maintaining the aluminum industry in a
healthy position to permit further expansion in the United States. This would
reverse the trend toward exporting technology and production to areas where
power is available at low cost.
The other area of research opportunity is a continuation of the Bureau of
Mines' recent efforts on developing means for producing alumina from domestic
raw materials, particularly kaolin and anorthosite clays. The situation could
be improved with respect to slowing the increasing cost of bauxite and alumina
imported from abroad, if it could be demonstrated on a sizable production unit
that the United States could produce alumina from its own domestic sources.
This would tend to deter future increases in taxes on bauxite and the foreign
exchange problem related to importation of alumina-bearing raw materials.
More specifically, we believe, because we have seen the results of recent work
on the nitric acid process, that much more of the thermal requirements for
these processes could be supplied by burning coal instead of natural gas.
Of course, as mentioned previously in this report, the development of
domestic reserves of alumina-based materials would be enhanced if the
depletion allowance on clays were increased.
Regrettably the clay processes, acid leaching, or the chlorination process
appear to offer no energy incentive over the existent Bayer process.
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APPENDIX A
INDUSTRY STRUCTURE - ALUMINUM
1. DESCRIPTION
The aluminum industry is comprised of two basic sectors: (1) the produc-
tion of alumina from bauxite by the Bayer process, and (2) the reduction of
alumina to aluminum metal by the Hall-Heroult electrolytic reduction process.
These two operations are conducted at entirely separate locations.
a. Alumina
Within the United States there are nine alumina production plants (see
Figure A-l). Eight of these are located in the continental United States and
the ninth is in the Virgin Islands on the island of St. Croix. Total alumina
production capacity of the industry is estimated at 7.7 million short tons
with individual plant capacities ranging from 1.385 million short ton/yr
(Reynold's Corpus Christi plant) to 370,000 short ton/yr (Martin Marietta's
plant at St. Croix) (see Table A-l). By modern standards the U.S. alumina
plants are considered small. Most new installations being built abroad start
at at least 1 million and more typically 2 million ton/yr capacity.
With the exception of the plant at St. Croix, which was built in the 1960's,
all of the present U.S. alumina plants are relatively old. The oldest plant
was built by Alcoa at Mobile, Alabama, in 1940; two more (Kaiser at Baton Rouge
and Reynolds at Hurricane Creek) were built prior to 1946, and the rest began
operating in the late 1940's and early 1950's.
Most of the alumina plants are located on the Gulf Coast because of the
availability of natural gas. The two plants in Arkansas, at Hurricane Creek
and Bauxite, were originally based on Arkansas bauxite, the only domestic
source of this raw material. As the quality of Arkansas bauxite has become
poorer, these plants have turned to foreign sources for part of their bauxite
supply.
Some alumina plants are located near aluminum smelters. At Point Comfort,
Texas, for example, Alcoa has both an alumina plant and an aluminum smelter.
The Reynolds alumina plant in Corpus Christi serves Alcoa's Texas smelters as
well as the Reynolds smelter in Corpus Christi. .Sources of alumina are there-
fore not always captive. Foreign alumina plants are often under joint owner-
ship. Since the establishment of a new alumina plant involves a major invest-
ment in mining and production facilities, it is often organized on the basis
of pay-or-take contracts with aluminum producers. Plants are not usually
designed and constructed until firm long-term commitments have been obtained
for marketing the alumina.
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LEGEND:
• ALUMINUM SMELTERS
• ALUMINA PLANTS
SAINT CROIX.
U.S. VIRGIN ISLANDS
Figure A-l. Location of Alumina Plants and Aluminum Smelters in the United States
-------
TABLE A-l
U.S. ALUMINA PLANTS
Location and Capacity - 1975
Short Ton/Yr
Aluminum Company of America
Mobile, AL 1,025,000
Bauxite, AR 375,000
Point Comfort, TX 1,350,000
Martin Marietta
St. Croix, VI 370,000
Kaiser Aluminum and Chemical
Baton Rouge, LA 1,025,000
Cramercy, LA 800,000
Reynolds Metals Company
Hurricane. Creek, AR 840,000
Corpus Christi, TX 1,385,000
Ormet Corporation
Burnside, LA 600.000
7,770,000
b. Aluminum
There are 31 aluminum plants in the United States, operated by 12 compan-
ies, 6 of which are also domestic alumina producers. These plants are located
primarily in three areas: along the Mississippi and Ohio Rivers, in the
Pacific Northwest, and in upper New York State at or near Massena, N. Y. (see
Figure A-l). Total aluminum production capacity in 1975 (see Table A-2) is
estimated at 5,019 million short tons, with individual plant capacities rang-
ing from 285,000 (Alcoa's plant at Rockdale, Texas) to 36,000 short ton/yr
(Consolidated Aluminum's Lake Charles, Louisiana plant).
The location of aluminum smelters is determined, by two factors: access
to river systems for transportation of alumina and availability of what was
originally low-cost power. Plants in Missouri, Kentucky, Indiana, Ohio,
West Virginia, Tennessee, North Carolina, and Alabama take advantage of both
the Mississippi-Ohio River transport system and the availability of low-cost
coal. The two plants in Massena, New York, have access to the St. Lawrence
River for transportation and low-cost hydroelectric power. Plants located
in Washington (7 plants), Oregon (2 plants), and western Montana (1 plant)
are also located near hydroelectric power.
Nine of the 31 smelters began operation prior to 1946 (see Table A-3).
Ten years later there were a total of 15 plants in operation, and by 1970,
11 more had begun producing aluminum. Soderberg and prebake smelters were
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TABLE A-2
U.S. ALUMINUM PLANTS
Location and Capacity - 1975
(1)
Aluminum Company of America^2)
Alcoa, IN
Badin, NC
Evansville, IN
Massena, NY
Point Comfort, TX
Rockdale, TX
Vancouver, WA
Wenatehee, HA
Anaconda Aluminum
Columbia Falls, MT
Sebree, KY
Consolidated Aluminum
New Johnsonville, TN
Lake Charles, LA
Martin Marietta
The Dalles, OR
Goldendale, WA
Eastalco
Frederick, MD
Incalco
Bellingham, HA
Kaiser Aluminum and Chemical
Chalmette, LA
Mead, HA
Ravenswood, WV
Tacoma, WA
Onnet
Hannibal, OH
Noranda
New Madrid, MO
National Southwire Aluminum
Hawesville, KY
Revere Copper and Brass
Scottsboro, AL
Reynolds Metals Company
Arkadelphia, AR
Corpus Christi, TX
Jones Mills, AR
Listerhill, AL
Longview, HA
Massena, NY
Troutdale, OR
Short Tons/Year
270,000
120,000
280,000
140,000<3)
285,000
115,000
180,000
120,000
141,000
36,000
90,000
115,000<6>
174,000<7>
260,000
260,000
220,000<8>
163,000
81,000
260,000<9>
70,000
180,000
114,000<10)
68,000
114,000
125,000
202,000
210,000
126,000
130,000
5,019,000
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TABLE A-2
U.S. ALUMINUM PLANTS
Location and Capacity - 1975 (Cont.)
Footnotes:
1. Unless otherwise indicated, no change in capacity between 1974 and 1975,
2. Total capacity for company in 1974 was 1,575,000 short tons/year.
1975 figures will be higher.
3. 1974 - 135,000 short tons/year. Increase due to improvements.
4. 1974 - 185,000 short tons/year. Decrease based on company report. No
further explanation available.
5. 1974 - 180,000 short tons/year. Increase due to improvements.
6. Bureau of Mines revised up to this figure from 111,000 short tons/year
for both 1974 and 1975.
7. 1974 - 88,000 short tons/year. Substantial increase due to possible
take-over by Alumax and addition of second pot line.
8. Bureau of Mines revised up to this figure from 206,000 short tons/year
for both 1974 and 1975.
9. 1974 - 250,000 short tons/year. Increase due to improvements.
10. 1974 - 112,000 short tons/year. Increase due to improvements.
Source: Bureau of Mines, Personal Communication.
94'
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TABLE A-3
U.S. ALUMINUM SMELTERS - AGE AND TECHNOLOGY
Company & Location
of Smelter
Aluminum Company of America
Alcoa, TN
Badin, NC
Evansville, IN
Massena, NY
Point Comfort, TX
Rockdale, TX
Vancouver, WA
Wenatchee, WA
Anaconda Aluminum
Columbia Falls, MT
Sebree, KY
Consolidated Aluminum
New Johnsonville, TN
Lake Charles, LA
Martin Marietta
The Dalles, OR
Goldendale, WA
Eastalco
Frederick, MD
Intalco
Bellingham, WA
Kaiser Aluminum
i
Chalmette, LA
Mead, WA
Ravenswood, WV
Tacoma, WA
Ormet
Hannibal, OH
Age
pre-1946
pre-1946
1960
pre-1946
& 1958
1950
1952
pre-1946
1952
1955
1973
1971
1971
1958
1971
1970
1966
1957
pre-1946
1957
pre-1946
1958
Smelter
Technology
PB
PB
PB
PB
VSS
PB
PB
PB
VSS
PB
VSS
PB
PB
HSS
PB
PB
HSS
PB
95
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TABLE A-3
U.S. ALUMINUM SMELTERS - AGE AND TECHNOLOGY (Cont.)
Noranda
New Madrid, MO 1971 PB
Revere Copper & Brass
Scottsboro, AL 1970 PB
Southwire
Hawesville, KY 1969 PB
Reynolds Metals Company
Arkadelphia, AR 1952 HSS
Corpus Christ!, TX 1952 HSS
Jones Mills, AR pre-1946 PB
Listerhill, AL pre-1946 HSS
Longview, WA pre-1946 HSS
Massena, NY 1959 HSS
Troutdale, OR 1959 PB
•PB = Prebaked
HSS = Horizontal Soderberg System
VSS = Vertical Soderberg System
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built in the 1940?s and 1950's, but in the last 15 years only prebake smel-
ters have been constructed.
3. Source of Raw Materials
Since 1.93 tons of alumina are required to produce 1 ton of aluminum, the
total alumina requirement of the U.S. aluminum industry, when operating at
full capacity, is 9,686,670 tons, 1,916,670 tons more alumina than can be pro-
duced domestically. Therefore, at full-capacity operation, 20% of the alumina
used in aluminum production would have to be imported from foreign sources,
primarily the Caribbean, northern South America, and Australia. Since the
only domestic source of bauxite for alumina production is Arkansas bauxite,
and since this has become increasingly poor in quality, having a high silica
content, virtually all alumina produced in the United States today is based
on bauxite imported primarily from the same source countries which also supply
alumina.
It is unlikely that new grassroot Bayer alumina plants will be built in
the United States to produce the alumina that is presently imported. The
bauxite-producing nations have come together in an OPEC-like organization and
are pressuring the aluminum companies to locate their alumina-producing opera-
tions near the source of the bauxite. This pressure is in the form of local
taxes imposed on the bauxite before it is shipped to the United States. (How-
ever, local taxes are also imposed on alumina before shipment to the United
States, and this is an incentive for U.S. producers to find alternative raw
materials within their own country on which to base aluminum production.)
Other incentives for converting bauxite to alumina at the source of the
bauxite include a reduction in the freight charges, availability of financing,
and lower cost labor in the bauxite-producing countries. Approximately 2 tons
of bauxite are required to produce 1 ton of alumina, making shipment of the
alumina rather than the bauxite less costly. Moreover, most of the bauxite-
producing countries are relatively undeveloped and, as such, are able to secure
loans from organizations, such as the World Bank, for the transportation and
infrastructure requirements (e.g., ports, roads, housing for workers, etc.) of
alumina production facilities unavailable to the United States. For these
reasons, current construction of alumina plants is largely overseas, engineered
by American, European, and Japanese aluminum producers. The only potential
alumina production expansion in the short term in the United States is produc-
tion based on domestic clay. This would represent a deterrent to increased
alumina and bauxite costs as the raw material would be domestically available.
2. ECONOMIC OUTLOOK
a. Consumption
From 1953 to 1973, world consumption of aluminum experienced a long-term
growth rate on the order of 10% per year. In the United States, consumption
has risen gradually over the years, except in the 1940's when it rose sharply
and then leveled off in response to wartime needs for aircraft production.
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Aluminum's growth has been due to a variety of factors, which differ in
importance for each market and application. In general, these factors involve
economics; physical, mechanical, and chemical properties; and esthetics.
Building and construction is the largest end-use for aluminum in the
United States, followed by transportation, the electrical industry, packaging,
and consumer durable goods. The two fastest growing markets are transportation
and packaging.
In the building industry, the two major applications for aluminum are in
windows and doors and in external cladding for walls and roofs. Aluminum is
used for primary construction and, even more widely, in renovating existing
(particularly residential) buildings. The recent growth in mobile homes has
benefited aluminum in the building market. The earliest transportation appli-
cations for aluminum were in aircraft, and the aeros'pace industry now accounts
for 50% of the total transportation category.
Bare overhead electrical transmission"and distribution lines were the
first applications in which the substitution of aluminum became a serious
threat to another material, in this case, copper. In the world, aluminum has
captured this market.
Packaging is the fastest growing major aluminum market. About 50% of the
aluminum used in packaging is in cans, including beverage cans, can ends, and
composite cans (a combination of paper and aluminum foil). Aluminum is also
used for many specialty cans, such as the rapidly growing, shallow-drawn cans
for single-portion servings. Aluminum has also been very successful in rigid
foil containers. Although aluminum has been substituted for traditional pack-
aging materials in many cases, much of its growth in the packaging market has
been attributable to development of new products and methods of packaging.
Aluminum's inroads into the durable goods market have been at the expense
of many other materials, primarily steel, wood, zinc, and brass.
Table A-4 shows U.S. aluminum shipments by market for the years 1972,
1973, and 1974 as well as the percentage of total shipments each market accounts
for. No significant changes in the market percentages are likely in 1975,
although there may be an increase in the use of aluminum in the auto industry.
A significant decrease in total shipments is expected, as a reflection of a
reduction in demand.
In the 1960's U.S. consumption grew by an average of 8% per year (compared
to rates of 4-5% per year for steel, copper, an'd nickel) and grew fr.om 48% of
world consumption in 1960 to 54% in 1965 before dropping back to 48% in 1969
(see Figure A-2). The dominant position of the United States in terms of
smelter capacity began to erode during the 1960's, as U.S. capacity fell from
53% of the world total in 1960 to 45% in 1970. The rate of smelter building
in the United States dropped from 13% per year in the 1950's to less than 6%
per year in the 1960's to 2.5% per year in the first half of the 1970's.
98
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TABLE A-4
U.S. ALUMINUM SHIPMENTS BY MARKET AND PERCENT OF MARKET
(000's short tons)
1972 _%_ 1973 % 1974 _%_
Building and construction 1,597 27 1,800 25 1,587 22
Transportation 1,112 18 1,404 19 1,225 18
Containers and packaging 905 15 1,028 14 1,125 17
Electrical 768 13 927 13 930 14
Consumer durables 563 9 669 9 578 9
Machinery and equipment 375 6 475 7 500 8
Exports 281 5 470 7 472 7
Other 414 7 435 6 373 5
Totals 6,015 100 7,208 100 6,790 100
Source: Engineering & Mining Journal, March 1975.
The improved profits of the 1950fs and the continuing growth of the 1960's
brought a number of new companies into the field. As a result, the percentage
of industry capacity owned by the three largest U.S. producers - Alcoa, Reynolds,
and Kaiser - was somewhat reduced (although still substantial).
Another change has been the growth in international investment by the
leading companies. For many years the North American producers obtained raw
materials from the United States and the Caribbean and carried out virtually
all of their smelting and semifabricating in North America; the European
producers used European ore and processing facilities; and both groups con-
centrated on supplying their respective markets. The remainder of the world
had relatively small demand. However, during the 1960's these companies found
it necessary to invest abroad at!all levels to develop new sources of raw
materials and to protect and develop ingot and semifabricating markets. The
U.S. producers now have about 15% of their smelter capacity outside the United
States.
The financial condition of the aluminum industry is a matter of growing
concern. The rapid rate of growth of the industry generated heavy capital
requirements. The industry's requirement of $1.50-2.00 of capital investment
per dollar of annual sales is about three times the average for all industry.
Since a major share of the industry's capital is borrowed, the high cost of
money has had a severe impact on aluminum costs.
99
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5000
4000
co
O
I-
t-
tr
O
CO
CO
Q
CO
D
O
I
3000
2000
1000
- PRODUCTION
- CONSUMPTION
(e) ESTIMATE
1960
1965
1970
1975
Figure A-2. U.S. Aluminum Production and Consumption - 1960-1975
100
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An unfortunate tendency until at least the mid-1960's was for companies to
make smelter investments to maintain market share rather than evaluating the
merits of each investment in its own right. The industry expected the healthy
profits of the 1950's to reappear. Instead of being concerned about the sizable
gaps between anticipated growth in demand and scheduled capacity additions which
were evident throughout the decade, the companies continued to compare future
demand with present capacity, a perspective which encouraged continued expansion.
Posted ingot prices served much the same end, suggesting to outsiders that there
were good profits to be made in aluminum smelting. However, actual prices were
well below posted prices and returns on investment were well below general
industry standards. The industry's overcapacity tendencies have also been
spurred by Government economic planners who felt that the national economy
would benefit from the existence of aluminum smelters and subsidized companies
to build them.
Unfortunately, small surpluses are enough to have substantial price impacts.
Heavy capital investment in alumina plants and smelters plus power contracts that
often allow for little consumption flexibility give the aluminum industry very
high fixed costs, which put great pressure on management to cut prices rather
than output. However, the market is relatively price insensitive in the short
term, and price cutting serves to reduce total industry revenues rather than
to expand the total market.
While the industry reduced smelting costs by roughly 10% during the 1960's,
ingot prices in real terms are below their 1960 levels. The United States
posted price in constant dollars is lower than in 1960 and in current dollars
is only l£/lb above the 1960 level.
b. Smelter Economics
The life of an alumina plant is generally very long. Most plants have
been expanded and some of the original equipment has been replaced. The life
of an aluminum smelter is really the life of a system: buildings, aluminum
calcination equipment (rotary kilns, presses, and ovens for making anodes),
the electrical equipment, transformers, rectifiers, busbars, cranes, docks,
railroad sidings, storage areas, silos, etc.
A cell has a definitive life. Most can operate almost without interruption
for three to four years, while more modern cells operate for four to six years.
At the end of a cell's life, it is removed from the line and rebricked and
rebuilt with new cathodes; i.e., completely refitted within the steel shell.
Over a period of 14 to 16 years, even the shells are replaced. Accordingly,
most of the original plants have been expanded by an addition of cell lines.
This has required increased power capacities and additional busbars, buildings,
and facilities for producing anodes.
Until recently, there has been no incentive to reduce power consumption.
Aluminum smelters have traditionally been located where power was cheap. In
many cases, aluminum smelters were located a considerable distance from markets
for aluminum. Today there is no really cheap power left; that which is theoret-
ically cheap is too inaccessible. As a result, freight costs, capital and
interest charges, and tariffs have also become important site selection factors.
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Although the Hall-Heroult process for the reduction of alumina to alumi-
num metal has not changed basically since its introduction over 70 years ago,
important design and engineering changes have evolved. During the past 40-50
years, commercial cells have increased in size from 8,000 to 170,000 amperes
and have diminished 35-40% in power consumption. Modern cell lines are more
mechanized, and labor requirements in the cell rooms have been reduced to a
minimum. In the 1960's production costs were reduced about 10%, but we believe
further reduction will be more limited in the 1970's.
Past improvements resulted from the competitive development of two ver-
sions of the Hall-Heroult cell, which differ mainly in the nature of the car-
bon anode: the Soderberg (continuous self-baking) type and the prebaked type.
The early, large (high-amperage) cells used Soderberg anodes because they pro-
vided low-current densities (prebaked anodes large enough for high-amperage
cells were originally difficult to produce) and the capital 'cost for a moderate-
sized plant was lower. However, industry has since learned how to make large
prebaked anodes and is building larger capacity reduction plants. We doubt
that any new Soderberg-type plants will be built because of their 2-10% higher
power consumption and also because they present more difficult air pollution
problems, consume greater amounts of carbon, and are more difficult to control
and automate.
Other means of cutting production costs have been under development for
a number of years, some of which are discussed in the body of this report.
In addition to the obvious influence of rising power and labor costs,
the industry is faced with two other problems that will put upward pressure
on production costs. The industry is entirely dependent on synthetic cryolite
for use as the reduction electrolyte. This material is produced from fluor-
spar, which is currently in tightening supply and whose price is increasing
because of its growing consumption in steelmaking. Also, aluminum plants have
been forced to install air and water pollution controls to eliminate fluoride
emissions. Although Alcoa has developed a process that simultaneously elimin-
ates fluoride emissions and produces aluminum fluoride for use in the bath
(and will make this method available to other companies who wish to use it),
the process would involve new capital costs. We believe the industry will
be hard pressed to offset all these higher cost influences by new production
economies in the 1970's.
U.S. aluminum smelting and semifabricating operations were relatively
unprofitable during the 1960's. Profits were made on raw materials and by
companies (principally Alcoa) with low-cost hydropower sources. During the
1970's there will be less opportunity for aluminum companies to acquire new
low-cost hydropower sources and growing pressure on raw material profitability.
Thus, producers will have to look to smelting and semifabricating for increased
profits to compensate for relative declines in other areas. The industry's
unsatisfactory earning performance is reflected .in the market values of thei
outstanding stock of the major aluminum companies, which are well below the
cost of replacing their smelter capacity alone.
102
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The aluminum industry needs substantially more investment money in the
1970's than it did in the 1960's. Raising capital in the amounts needed will
be made more difficult by high interest rates and the industry's lackluster
earnings record.
Of the available options for improving profitability, substantial cost
reduction does not appear promising, especially in view of rising power costs.
While the outlook for alumina'prices is clouded, we see no grounds to assume
a change that will improve the profitability of the U.S. majors.
The long-term price level for aluminum (see Figure A-3) is influenced by
many, often conflicting pressures, including costs, profit levels, competition
with other materials, the international supply-demand balance, and industry
competition. The aluminum industry has grown rapidly by making metal avail-
able when it was needed and at a price which made it economically attractive
to use. If supply were allowed to drop below demand for an appreciable period,
list price would fluctuate considerably and some of the incentive to use
aluminum would be lost'. In applications where aluminum competes with copper,
aluminum has historically had an advantage in its relatively stable price.
A number of current trends weigh both for and against higher ingot prices.
On the positive side, the industry is showing some signs that it might be
better at handling overcapacity than it was in the 1960's. The share of world
smelter capacity accounted for by the major North American companies has
dropped sharply in recent years and is scheduled to drop even more in the
1970's. This trend suggests that these companies are now concentrating more
on the profitability of investments rather than on maintenance of market share.
Also, they have shown more willingness to take capacity out of circulation
early in an adverse supply/demand trend than has ever been the case before.
The present low earnings performance of the industry will create pressure
for higher prices as companies find difficulty in raising money. Unfortuna-
tely this natural market force is weakened by the availability of "political"
capital in countries where the creation of jobs and industrial activity are
more important than the profitability of the project. The industry must do
its utmost to convince international loan agencies and governments that smelters
should not be built before economic sales outlets are established.
Several negative pressures confront the move to raise ingot prices. The
principal one is a projected overcapacity. The 1974-75 downturn in U.S. con-
sumption has created a gap. Despite the significant production cutbacks men-
tioned earlier, prices have weakened from 1969-1970 levels, and we do not
expect prices to improve much until demand picks up substantially.
Another negative factor is the number of independent smelters around the
world that may not resist the temptation to emphasize volume rather than price
improvement once demand strengthens. Even the major companies will experience
difficulty in restraining their production to coincide with consumption.
103
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50
£
LU
o
20
I
I
I
I
I
I
I
I
I
J
1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975
SOURCE: ENGINEERING & MINING JOURNAL, MARCH 1975
Figure A-3. Annual Average Price Aluminum - 1910-1974
104
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c. Leading Companies
The structure of the world aluminum industry is becoming significantly
less concentrated as investments are distributed across more countries and
among more companies. The tendency to integrate operations is expected to
continue, but will more likely involve large consumers integrating backward
rather than ingot producers adding substantially to captive outlets. New
participants will probably continue to enter the industry, especially in
raw material ventures and in combined smelter/semifabricating facilities.
The four major North American aluminum companies - Alcoa, Alcan, Reynolds,
and Kaiser - are also the largest aluminum producers in the world.
105
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APPENDIX B
PRESENT TECHNOLOGY
1. RAW MATERIALS
The major raw materials for the primary U.S. aluminum industry are
imported alumina and imported bauxite, which is domestically refined to
alumina. In addition to these basic raw materials, there is some small pro-
duction of alumina from alunite based upon a small pilot plant operating at
Golden, Colorado. However, for all practical purposes-, the alumina for the
U.S. market is produced by Bayer process based upon imported bauxite. This
is the first step in the domestic primary aluminum industry.
2. DESCRIPTION OF MAJOR PROCESSES
a". Refining of Bauxite to Alumina via the Bayer Process (Figure B-l)
(1") Digestion
In the Bayer process, finely ground bauxite (-35 mesh), usually wet
ground in spent digestion liquor, is digested at elevated temperatures under
pressure. The digesting liquor contains sodium aluminate and free caustic.
In this operation the alumina hydrate in the bauxite is dissolved by the
free caustic as sodium aluminate according to the following reaction:
Al203.xH20 + 2NaOK -> 2NaA102 4- (x+1) H20
The solubility of alumina (A1203) increases with temperature and caustic con-
centration. Bauxites used in the production of alumina contain alumina trihydrate
(A1203.3H20) and alumina monohydrate (A1203.1H20) . Optimum reaction conditions
vary with the hydrate type as follows:
Trihydrate: 128-192 g/1 NaOH @ 250°-340°F (50-60 psi) ,
Monohydrate: 257-389 g/1 NaOH @ 390°-570°F (up to 500 psi) .
The U.S. industry has historically been based on bauxites from the Caribbean
which are primarily trihydrates, whereas the European industry has historically
been based more on bauxites that are typically much higher in monohydrate. Tri-
hydrate ores are, of course, preferred because of milder operating conditions;
however, the use of ores with increasing amounts of monohydrate is becoming
necessary in the U.S. and Caribbean alumina plants. The average monohydrate con-
tent of bauxites presently imported into the United States is 15-20%. To obtain
high alumina recovery from these materials requires higher digestion tempera-
tures and pressures. Digestion temperatures of 400°F and 200 psi are now
becoming common in the U.S. Bayer alumina plants.
106
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Figure B-l. Bayer Process for Producing Alumina
107
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(2) Removal of Impurities
After the digestion step, the insoluble components of the bauxite,
primarily the oxides of iron, silica, and titanium, are removed by thick-
ening and filtration. The separated solids, known as red mud, are discarded.
Silica is a paritcularly undesirable impurity in bauxite, especially in the
form of clay, since it is readily dissolved in the caustic liquor. Although
silica is rapidly rejected from solution as a complex sodium aluminum silicate
(3Na20.3Al203.5Si02.5H20), these sodium aluminum silicates cause problems with
equipment scaling and filtration and the precipitate carries with it propor-
tionate amounts of alumina and sodium.
The Bayer process can be modified, i.e., the so-called combination process
which permits a treatment of high-silica bauxites. However, in the United
States this process is used only on high-silica domestic ores which produce
alumina that largely goes into the production of refractories and uses other
than that to produce aluminum metal.
However, any silica present in the bauxites is rejected as sodium
aluminum silicates which carry out sodium in the red mud. Also, a small
amount of uncombined caustic soda is lost to the red mud in spite of water
washing the red mud filter cake on the filters prior to final disposal.
Following digestion, which requires approximately one hour, the caustic
slurry is cooled to its atmospheric pressure boiling point of about 250°F in
a series of flash tanks. The steam flashed off during cooling is used to
preheat the new fresh bauxite-caustic mixture prior to entry into the digesters.
The digestion temperature is obtained either by steam-jacketing the reaction
units or, More commonly, by direct injection of steam. After cooling, the
residue (red mud) is removed from the caustic slurry in thickeners followed
by filtration of the red mud underflow. Ten to 20 pounds of starch are used
as a flocculating agent to help settle the'red mud in the thickeners. Dilution
with warm water or spent liquor is also used to aid separation of the red mud
from the pregnant liquor. The red mud discharged from the thickener goes to a
mud washer filter where the mud is washed with water to recover sodium hydroxide
which goes back to the thickener and into the main pregnant liquor process
stream. The quantity of red mud removed from the caustic slurry following
digestion varies with the bauxite used and can range from 0.33-2 tons per ton
of alumina produced. About 0.8 ton of red mud per ton of alumina is typical
in U.S. plants.
(3) Precipitation
The resulting main process stream sodium aluminate solution goes to a
clarifying filter and the clarified "green liquor" then goes to precipitation.
This liquor, now clarified and diluted, is cooled in a heat exchanger to 120°-
140°F and placed into large precipitation vessels that are seeded with alumina
trihydrate crystals and mildly agitated to precipitate dissolved alumina tri-r
hydrate, according to the following reaction:
2NaA102 + 4H20 -»• AlgOg.SHgO + 2NaOH.
108
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Approximately 50% of the alumina is precipitated during a 34-36 hour period in
the precipitation vessels. The resulting trihydrate is separated by settling
and filtration. A portion of this precipitate is stored and used to seed sub-
sequent green liquor. The product trihydrate is finally washed to minimize
caustic soda losses during the filtration step. Spent liquor goes on to a
spent liquor treatment operation and the product (washed alumina hydrate) goes
to calcination.
(4) Spent Liquor Treatment
Spent liquor is a caustic solution containing about half of the sodium
aluminate originally present before precipitation. This is recycled to the
process for reuse. The uncombined caustic content of this solution will be low
as a result of dilution during settling and filtration, and losses of soda as
complex sodium aluminum silicates removed in the red mud. However, this spent
liquor represents a large inventory of sodium aluminate that is still present
in the solution. The free caustic content of this recycle liquor is increased
by a combination of evaporation of excess water and the addition of makeup caus
tic to increase the caustic concentration to the desired level of digestion.
Caustic makeup may be accomplished by adding caustic soda directly, but
more typically it is produced in the process by addition of lime and soda ash
according to the following reaction:
NaCO + CaO + H0 -> ZNaOH +
The latter method is presently preferred and is used almost exclusively now in
the United States because the alumina plants have found it difficult to obtain
caustic soda and because lime is required in any case to causticize the sodium
carbonate formed in the process. Typically, a portion of the spent liquor is
taken off at this point and evaporated to higher concentrations to precipitate
sulfates which tend to build up in the system with time. Sulfates may also be
controlled by contact of the spent liquor with red mud during the clarification
step by use of spent liquor for dilution.
The consumption of chemicals is also a function of the composition of the
bauxite. Most of the caustic soda is recycled but makeup is required to replace
losses and the amount consumed by the silica as sodium aluminum silicate. The
loss of caustic is approximately equivalent to 90% of the silica content of the
bauxite. Typical makeup requirements per ton of aluminum produced are 100-200
pounds of soda ash and about the same amount of calcined lime. Lime used in
the Bayer process is usually obtained from selected high-grade limestone calcined
at the quarry or at the Bayer plants. It requires about 1.8 tons of limestone
to produce a ton of lime.
The range of soda ash and lime requirements (Ib per ton of alumina) are as
follows :
Soda ash 100-200 Ib
Lime 100-200 Ib.
Limestone requirements to produce the above amount of 'lime are 180-360 Ib of
limestone per ton of alumina.
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(5) Calcination
In most U.S. Bayer alumina plants, the resulting alumina hydrate is calcined
to rotary kilns which operate at about 2100 °F to remove moisture and water of
hydration. The resulting alumina is so-called pot feed alumina, which is the
raw material for the production of aluminum metal via the Hall-Heroult electro-
lytic reduction process.
(6) Raw Materials Consumption
Bayer plant operations vary since bauxite used from the several Caribbean
sources differs in composition and causes variations in the consumption of raw
materials, chemicals, and thermal energy. The bauxite required to produce a ton
of alumina via the Bayer process depends upon the alumina content of the bauxite,
the amount of trihydrate and monohydrate present, and the impurities, such as
silica, iron, and titanium.
(7) Power Consumption
The power consumption in the Bayer plants is mainly for grinding the
bauxite, with lesser quantities used for grinding lime and for driving mixers,
rotary kilns, pumps, etc. The power consumption for grinding is a function of
the hardness of the bauxite. Power consumption per ton of alumina has been
variously estimated at 160-300 kWh/ton of alumina. These estimates have been
made on the assumption of trihydrate bauxite feed to the plant, and on the basis
that it is previously crushed. With monohydrate bauxite, power consumption for
grinding is as much as 40% greater. The above range of estimates of power con-
sumption per ton of aluminum is based upon a crushed bauxite. It does not
include any power costs for crushing. Actually, about one-quarter of the
bauxite imported into the United States is in the form of crude, undried,
uncrushed bauxite. If one takes this into account and the fact that these
imports contain up to 15-20% monohydrate, we believe that the average power
consumption per ton of aluminum is more nearly 275 kWh/ton of aluminum than the
consumption estimated previously by others.
(8) Fuel Consumption
Fuel is used in the refining stage mainly to generate steam for digestion
and evaporation and also for firing the calcining kilns. Steam consumption has
been estimated to vary as follows:
Trihydrate-based bauxite plants - 3000-8000 Ib steam/ton alumina, and
Monohydrate-based bauxite plants - 4500-14,000 Ib steam/ton alumina.
Most of the major alumina producers have their own limestone quarries
because a high grade of lime, and thus limestone, is required to avoid intro-
duction of impurities into the system. The lime calcination is carried out at
the quarry or at the aluminum plant and therefore is an energy requirement of
the process.
110
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Since limestone requirements range from 0.09-0.18 ton per ton of
alumina and the heat requirements for calcination are 4.25 x 10^ Btu per
1.8 tons of limestone, the thermal energy requirements for lime calcination
range from 0.21-0.43 x 10^ Btu per ton of alumina.
There is also a thermal energy requirement for the calcination of
alumina which has been variously estimated to range from 2.7-5.0 x 106 Btu
per ton of alumina, depending on the size and efficiency of the calcination
system. We believe that the average fuel requirement for calcination in the
U.S. Bayer plants is about 4.0 x 10^ Btu per ton of alumina.
Table B-l summarizes the ranges of materials and energy requirements
in U.S. alumina plants and the considered averages.
TABLE B-l
BAYER ALUMINA PRODUCTION
RANGE OF REQUIREMENTS AND CONSIDERED AVERAGE REQUIREMENTS
Present U.S. Operations - Conventional Technology
Considered
U.S. Industry Average
Raw Materials:
Bauxite
Limestone
Soda ash
Starch.
ton/ton Alumina
.09 - .18
.05 - .1
.005- .01
ton/ton Alumina
2.40
.133
.075
.006
Power:
kWh/ton Alumina
200 - 300
kWh/ton Alumina
275
Fuel:
Steam generation
Lime calcination
Alumina calcination
TOTAL
106 Btu/ton Alumina 106 Btu/ton Alumina
4.4 - 11.3
.21 - .43
2.8 - 5.0
7.33
.31
4.00
11.64
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b. Hall-Heroult Reduction. Process
There are 31 U.S. aluminum reduction plants producing primary aluminum
from refined alumina. All of these use the conventional Hall-Heroult process.
(1) Electrolytic Reduction
This is an electrolytic reduction process in which alumina is continu-
ously dissolved in molten cryolite in the cell wherein aluminum is liberated
at the cathode and oxygen at the anode. The oxygen liberated at the anode
reacts with the carbon anode to produce CC>2 and CO. The overall reaction for
the reduction of alumina by the Hall-Heroult process is as follows:
2A1203 + 3C •*• 4A1 + 3C02
The anode gas will also contain some CO as the result of back reaction of
aluminum dissolved in the electrolyte reacting with COo as follows:
3C02 + 2A1 -> A1203 + 3CO
The anode gas is typically 50% by volume C02 and 50% CO.
The basis of this process is that alumina (A1203) dissolves readily in
molten cryolite (Na3AlFg), forming a eutectic at 16% A1203 at 1725°F. The
electrolytic reduction is conducted at 4.6 volts and at or near the tempera-
ture of the electrolyte. The cell electrolyte contains 80-85% cryolite, 5-7%
calcium fluoride (CaF2), 5-7% aluminum fluoride (A1F3), and 2-8% alumina.
(^) Hall-Heroult Cells
Modern Hall-Heroult electrolytic cells are large steel boxes lined with
insulating refractory and carbon. Carbon blocks at the bottom of the cell serve
as the cathode in the electric circuit. During electrolytic reduction,
aluminum metal in molten form is deposited as liquid at the bottom of the
cell on the surface of the carbon cathode. This pool of molten aluminum is
the active cathode resting upon the carbon cathode blocks at the bottom of
the cell which form a connector to steel conductor support members which
eventually connect to the cathode bus. Cathodes are more or less a permanent
installation. Typically, the cathodes last three to six years, about the same
as the life of the cell itself, after which time the cell is taken out of
service, rebuilt, and refitted. Cathodes are purchased from carbon producers,
while anodes are produced at the aluminum plants.
(3) Anode Systems
The anodes are also carbon suspended in the electroylte from above on
steel connector rods that connect to the anode bus. The carbon anodes used in
the reduction cells are produced by two methods, Soderberg or prebake. In
both systems a combination of petroleum pitch and petroleum coke is used to pro-
duce the anodes.' In the Soderberg system, so-called Soderberg paste is fed
continuously into the top of the steel Soderberg casing in which the heat from
-112
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the cell and current flow bakes the paste and removes the volatiles. In the
prebake system, the volatiles are removed by making the anodes in a separate
anode-forming prebaking operation.
The prebake system has a number of advantages over the Soderberg system.
It requires significantly less energy than the Soderberg system and, because
the anodes are baked in separate facilities, it is easier to recover the
volatiles released from the anode paste.
In the Soderberg system where the prebaking of the anodes is occurring
above the cell, it is complicated and difficult to recover the volatile hydro-
carbons in the presence of fluorine and fluorides, CC>2 and CO, by a simple
collection system. Also, power consumption is higher in Soderberg systems
because expensive electrical energy is used to bake the paste. For these
reasons, it appears that the prebake system will be used in new facilities and
may eventually be substituted for Soderberg systems in existing plants.
Of the two anode systems used, the prebake system is the older of the
two, but in the past the Soderberg system had two main advantages:
• Capital costs were lower for small smelters, because the
Soderberg system avoided the cost of separate anode-making and
-baking facilities; and
• It was easier to produce large cross sectional block anodes that
were required in large cells.
By way of further explanation, the Soderberg system uses an anode which
is baked by the reaction heat from the cell itself and resistance heat gener-
ated by the current passing through the paste. The carbon paste is used as
the anode material and is fed to the top of the anode casing. As the paste
moves down, it is baked, forms the anode, and then is consumed as carbon
doxide is formed and released. The carbon that is removed is replaced by the
paste injected into the top of the anode and thus becomes a continuous anode-
making process.
(4) Production of Prebaked Anodes
In the prebake system, prebaked anodes are manufactured in a separate
installation from high-purity petroleum coke, which is ground, calcined, and
blended with pitch to produce a paste which can be pressed into high-density
shapes. Approximately 1975 pounds of petroleum coke plus about 444 pounds of
pitch are required to produce a ton of anode carbon. The coke is either
purchased calcined or is calcined at the plant and ground, and is mixed with
pitch in a ratio of about 4 pounds of ground, calcined coke to 1 pound of pitch.
This is mixed and pressed into shapes of the required anodes. The pressed
anode blocks are then baked^at temperatures up to 2000°F for periods as long
as 30 days (baking and cooling period) and fitted with steel connector rods
which support the anode and provide a connection to the anode bus. Molten cast
iron is poured into the anode socket to make a good electrical connection
between the steel rod and the carbon anode. As mentioned above, these anodes
are consumed by oxidation of the carbon and are replaced as required to prevent
the steel from contaminating the cell electrolyte and the aluminum.
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(5) Cell Operation
Aluminum reduction cells operate continuously with periodic additions
of alumina and electrolyte additives, replacement of anodes, and removal of
molten aluminum. Aluminum is removed periodically at one- to three-day
intervals and blended with the output of other cells to attain a uniform
purity level. The blended material is degassed and cast into ingots or sows
or is delivered as molten metal to fabricating plants.
In addition to aluminum additions, there are periodic additions of fluor-
spar, namely, calcium fluoride (CaF2), aluminum fluoride (A1F3), and cryolite
(Na3AlFg), to make up fluorine losses. Fluorine is released at the anode from
partial reduction of the electrolyte. Approximately 50 pounds of fluorine are
released per ton of aluminum produced.
(6) Energy Consumption
(a) Electric Power
Energy is consumed primarily in the form of electric power, but thermal
energy is also required for anode baking and casting. Modern Hall-Heroult
cells, using a prebaked anode system, typically draw 150,000-160,000 amperes
operating across a relatively small voltage drop, typically in the range of
4-5 volts; a 4.6-4.7 voltage range is common in the U.S. industry. The smelt-
ing step is by far the most energy-intensive in the aluminum production
sequence. Power consumption per short ton of aluminum ranges broadly from a
low of 12,400 to as high as 20,000 kWh/short ton of aluminum. Historically,
the United States has had the advantage of relatively low power costs, so that
power consumption has been moderately high, in the range of 14,000 to 18,000
kWh/short ton of aluminum. The average is currently about 15,600 kWh/short ton.
Power consumption in the smelting of alumina to aluminum metal is basically
the result of a trade-off between power costs and capital investments required
in the cell. In France and Switzerland, the power costs have been relatively
high. Producers have reduced power consumption considerably - to the range of
12,400 to 13,600 kWh/short ton. On the other hand, countries with cheap power
costs, such as Canada and Norway, report 15,000 to 17,250 kWh/ton. We have
recently had reports that in the best cell lines power consumption can be as
low as 12,000 kWh/ton in prebaked Hall-Heroult type cells. This is about the
minimum attained to date in the most modern cells. It is a target that could
be reached if all the cell lines were modernized by installation of large
Hall-Heroult type prebaked cells using the most modern present day technology.
This would require an enormous investment by industry and would be difficult
to justify, unless the cost of power increases very dramatically, at which
time the oldest, most inefficient plants would be modernized or closed down.
(b) Fuel
In addition to the power required in the aluminum smelters, there is also
the requirement for thermal energy for calcining green coke and baking anodes
and for casting sows or semifinished forms.
114
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Most aluminum smelters today are purchasing calcined coke so the energy
requirements for calcination of petroleum coke are presently being carried
out at the refineries prior to shipment to the aluminum smelters. The fuel
for calcination is no longer a major consideration at the smelter. With the
fuel availability and waste gases and waste heat at the refinery, the calcina-
tion is more logically carried out on a larger scale at the refinery rather
than on a small scale at the carbon plants of the aluminum smelters.
However, there is ah energy requirement for the production of the pre-
baked anodes. It has been variously estimated to be in the range of 2.3 to
3.6 x 10" Btu/ton of aluminum. We believe that the average requirement in
modern baking installations would amount to about 2.6 x 106 Btu/ton of alumi-
num. This is the net energy input to the baking, i.e., external fuel used in
baking. Combustible gases and part of the tar used in the anode forming are
baked out in the anode-baking operation and burned at the top of the baking
ovens with air lances to control pollution emissions and provide some direct
heat to the baking. The amounts lost are modest, roughly 222 Ib of material
per ton of anodes, but onLy amounting to about 100 Ib of fossil fuel values
per ton of aluminum. The Btu value of the material would be about 10,000 -
12,000 Btu/lb, but it would be extremely difficult in the typical layout baking
operation to recover this material.
Requirements for casting range from 1.5 x 10 Btu/ton of aluminum for
simple casting of the aluminum metal in the form of sows to a requirement of
11 x 10° Btu for production of semifinished forms such as a product mix of
35% rolling slabs, 35% extrusion billets, and 30% sows. We believe, however,
that the average is about 4 x 10^ Btu/ton of aluminum for casting. This means
that the total average thermal energy requirement is 6.6 x 10 Btu/ton.
Table B-2 presents a range of materials added per ton of alumina and the
considered average additions or consumptions of alumina, cryolite, aluminum
fluoride, calcium fluoride, petroleum coke, and petroleum pitch. It also
presents the range of power and fuel consumption and considered averages in
U.S. smelters.
(7) Energy Conservation - Existing Plants
It is well recognized that the major energy-consumption in the aluminum
industry is in the reduction cells. In theory, the minimum amount of energy
required to produce aluminum from alumina in the cell is about 35% of that
used in the present electrolytic process. There are two main reasons for the
relative inefficiency in comparison to theory of present electrolytic Hall-
Heroult reduction cells. These are: (1) the back reaction of aluminum at the
anode with C09, forming alumina and CO; and (2) the resistance in the cell
electrolyte and the anode and cathode hardware.
The back reaction of aluminum to alumina results from molten aluminum in
the cathode pool agitated by the large current flux to the anode where it
reacts with C02 to form CO and alumina. This back reaction reduces the
Faraday efficiency of the cell interface where the back reaction occurs.
Increasing the distance between the anode and cathode reduces this back
reaction, but it also increases the voltage drop (resistance) across the
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TABLE B-2
HALL-HEROULT ALUMINUM SMELTING RANGE OF REQUIREMENTS AND
CONSIDERED AVERAGE REQUIREMENTS
Present U.S. Prebaked Plant Operation - Conventional Technology
Range
Considered
U.S. Industry Average
Raw Materials:
Alumina
Calcined petroleum coke
Pitch
Cryolite
Aluminum fluoride
Calcium fluoride
ton/ton of Aluminum
1.91 - 1.95
0.43 - 0.60
0.10 - 0.20
0.01 - 0.05
0.01 - 0.05
ton/ton of Aluminum
1.93
0.52
0.15
0.035
0.02
0.003
Power:
Fuel:
Baking anodes
Casting
kWh/ton of Aluminum kWh/ton of Aluminum
14,000 - 18,000 15,600
3^ Btu/ton of Aluminum 10 Btu/ton of Aluminum
2.3 - 3.6 2.6
1.5 - 11.0
1.5
(*)
Simple casting of sows.
electrolyte. A more practical measure would be to reduce the turbulence of
the metal and the electrolyte interface where the back reaction occurs.
Improved stability of the molten aluminum pad can be achieved by operation at
the lowest possible temperature that will maintain the electrolyte in a liquid
state and constant control of alumina concentration. Over the past 20 years,
back reaction has been reduced by 10-20%.
It is well known that if the anode current density is reduced, the turbu-
lence of the bath between the anode and cathode can be reduced, as a result of
which the back reaction is-reduced slightly. Alternatively, the anode/cathode
116
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distance can be reduced, as a result of which the voltage drop across the
bath becomes lower and the power consumption per ton of aluminum is reduced.
In either case, the power input to the cell is lower and therefore production
rates are lower. For example, by reducing the anode current density by 20%,
one can expect an increase in efficiency of about 15%. However, if production
is to be maintained, more cells would have to be added. Thus more investment
is necessary to reduce power consumption, and this is the trade-off that must
be made in an existing operation.
Moreover, any substantial reduction in current flow or voltage drop to
the cell will produce a drop in the heat generated in the cell. To continue
to maintain the necessary high operating temperatures, typically 1650°F, in tne
cell, after such improvements, heat losses would have to be reduced. This can
be accomplished by increasing side and bottom insulation which, of course,
requires additional capital investments.
Small energy savings can be achieved through better control of the cell
operating parameters. One company reports a 3% improvement in energy through
better control of the molten aluminum pad depth, the anode/cathode distance,
and more frequent additions of alumina in the cell.
Quality control of anode baking should improve operating uniformity and
could reduce the voltage drop in the anode. A total of all of these measures
could reduce consumption in existing plants by 5-10%.
Some longer range improvements can be attained in the overall situation,
since the newest smelters that have come on line in recent years have exhibited
energy-consumption rates of between 6 and 7 kWh/lb of metal. This is an
efficiency improvement of about 15-20% over past average smelter efficiencies
due to the application of a number of measures to reduce the voltage drop,
e.g., decreasing back reaction and better control of operating parameters.
Until recently, it was thought that energy conservation would be improved
in the industry if existing Soderberg processes, which have tended historically
to be higher in energy consumption, were replaced with prebake systems.
However, one company (Japan's Sumitomo Chemical) is licensing the technology
for a modified Soderberg system that involves a series of relatively small
modifications that combine to provide a claimed 12-20% reduction in power con-
sumption, a 50-100% extension of cell life, and sizable reductions in emissions
of hydrocarbons and fluoride gases, plus a reduction in labor requirements.
This company will discuss few details of its improvements, which include
changes in operating procedures as well as equipment design but a process
description is given in Chemical and Engineering News (August 4, 1975;
American Chemical Society). Sumitomo claims 14,000 kWh/metric ton,of aluminum,
which amounts to 12,700 kWh/short ton as compared with U.S. and European
Soderberg cells that operate in the range of 14,500 to 16,300 kWh/short ton
of aluminum. The company claims that this results from a series of improve-
ments, such as improved cell stability minimizing voltage fluctuations.
Typical drops across the Soderberg cells are 4.7-5 volts, depending on
the alumina content of the electrolyte. When the alumina content of the
electrolyte falls below 1%, the voltage can rise rapidly, as much as 30 volts;
117
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at 100,000-165,000 amperes, small changes in voltage drop mean major changes
in power consumption per ton of aluminum produced. For example, an average
reduction of 1 volt out of 5 volts is a 20% effect and would have a 20% effect
on power consumption.
The means of controlling voltage fluctuations are: (1) control of
alumina content of the electrolyte to proper levels i-by more frequent alumina
additions, and (2) altering the heat balance to the cathode by matching a
given cathode material with a proper insulation configuration to optimize
temperature differences throughout the cathode. Control of voltage fluctua-
tions can have the following effects: (1) prolonging the working life of the
cathode blocks from a previous average of 3-4 years before lining failure and
shutdown,* and (2) reducing operating maintenance labor from about 1.4 to
about 0.65 man-hours per short ton.
*The average life of modified cells in one company's plants is now about 6
years, which is double the previous life, and has been as high as 8 years.
118'
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APPENDIX C
CURRENT POLLUTION PROBLEMS AND
EFFECTIVENESS OF AVAILABLE POLLUTION CONTROL TECHNOLOGY
1. WATER POLLUTION
Water pollution regulatory constraints imposed upon the bauxite refining
and primary aluminum smelting segments of the aluminum industry are mainly
the result of Sections 304 (b) and 306 of the Federal Water Pollution Control
Act, as amended. The Act provides for the Environmental Protection Agency
to issue effluent limitations guidelines applicable to the point source dis-
charge of industrial wastewater. For specific industry categories, the
effluent limitation guidelines are based on technical studies commonly refer-
red to as the "EPA Development Documents." The function of the Development
Document is to characterize the industry, describe the sources of water pollu-
tion, the wastewater characteristics, control technology currently in use,
suggested permissible effluent levels, recommended technology for their
attainment, and cost estimates for the implementation of such technology.
For this study, general information on the sources of wastewater, waste-
water characteristics, treatment technology, and treatment cost estimates
has been extracted from the Development Documents pertaining to the bauxite
refining* and primary aluminum smelting** segments of the aluminum
industry.
a. Bauxite Refining
(1) Present Sources of Wastewater
The principal waste streams in the refining of bauxite using the Bayer
process are:
• Red-mud stream,
• Spent liquor,
*"Development Document for Proposed Effluent Limitations Guidelines and New
Source Performance Standards for the Bauxite Refining Subcategory of the
Aluminum Segment of the Nonferrous Metals Manufacturing Point Source
Category," U.S. Environmental Protection Agency, EPA 440/1-73/019, October,
1973.
**"Development Document for Proposed Effluent Limitations Guidelines and New
Source Performance Standards for the Primary Aluminum Smelting Subcategory
of the Aluminum Segment of the Nonferrous Metals Manufacturing Point Source
Category," U.S. Environmental Protection Agency, EPA/440/l-73/019a, October,
1973.
119
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• Condensates,
• Barometric condenser cooling water,
• Miscellaneous cooling-water streams,
• Miscellaneous waste streams, and
• Storm water run-off.
Each is briefly described below:
Red-Mud Stream
Red-mud is the insoluble residue remaining after extraction of the alumina
from bauxite. After filtration or thickening to separate the pregnant sodium
aluminate liquor from the red-mud gangue, the mud is pumped to disposal. If
not already at a pumpable consistency, it is first diluted. Depending on the
specific bauxite ore used, the residue may range between 0.33 to 2.0 tons per
ton of aluminum produced. The red-mud is typically disposed in a large red-
mud lake where the solids settle and the transport water is recycled.
Spent Liquor
To ensure proper process control, it is necessary to purge soluble con-
taminants that build up in the aluminum hydroxide precipitation circuit. This
is sometimes done by evaporation and results in a salt slurry that must be
disposed of.
Condensates
The bauxite refining process uses a large amount of steam in the numerous
heating and evaporation steps. Most of the steam is generally condensed and
reused for various plant operations, i.e., boiler feedwater and product
washing. In some plants where the water balance is excess, some Condensates
may be rejected as a wastewater stream.
Barometric Condenser Cooling Water
Barometric condensers are widely used in the bauxite refining industry
and are large consumers of water. In plants with an excess water balance a
certain portion of barometric condenser cooling water is rejected as a waste-
water stream.
Miscellaneous Cooling Water Streams
In bauxite refining there is typically a certain amount of non-contact
cooling water used for air compressors and other cooling duties.
Storm Water Run-off
Bauxite refinery sites occupy large areas. Depending on local climatic
conditions, storm water run-off can comprise a significant fraction of the total
wastewater stream. Typically, storm water run-off is collected, but during
heavy rainfall events excess stormwater must be diverted and discharged.
- 120
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2. Waste Characteristics
Red-Mud
Red-mud consists of a solid fraction composed of insoluble particles and
a soluble fraction. Table C-l shows a representation composition of these two
fractions:
TABLE C-l
**
REPRESENTATIVE COMPOSITION OF RED-MUD
Insoluble Fraction Soluble Fraction
Si°2 5.5% A1203 2.5g/kg liquid
A12°3 12.0% NaOH 3.7g/kg
Fe2°3 49-5* Na2C03 1.6g/kg
P2°5 2-0% Na2S04 0.4g/kg
CaO 8.0% NaCl 0.7g/kg
Na2° 3.5% Na2C204 O.lg/kg
Ti02 5.0% pH 12.5
Mn02 1.0% BOD 6 ppm
Miscellaneous (including COD 148 ppm
eo3 =) 1.5%
Loss on Ignition 11.0%
Spent Liquor
Salts from the salting-out evaporator purge step consist mostly of
alkaline ^2804.
Condensates and Cooling Water Streams
These streams may be slightly contaminated with alkaline dusts.
3. Effluent Limitations
In effect there is a single effluent limitation applicable to the
bauxite refining segment.* This limitation covers all three effluent
treatment levels, i.e.:
a. Best Practicable Control Technology Currently Available (to be
implemented by 1977),
*Federal Register, April 8, 1975 and April 10, 1975.
**Source: EPA Development Document.
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b. Best Available Technology Economically Achievable (to be implemented
by 1983), and
c. Standards of Performance for New Sources (applicable to plants
constructed prior to 1983),
and reads as follows:
"(a) Subject to the provisions of paragraph (b) of this section, the
following limitations establish the quantity or quality of
pollutant properties which may be discharged by a point source
subject to the provisions of this subpart after application of the
best practicable control technology currently available: There shall
be no discharge of process wastewater pollutants to navigable
waters.
Cb) During any calendar month where may be discharged from the over-
flow of a process wastewater impoundment either a volume of
process wastewater equal to the difference between the precipita-
tion for that month that falls within the impoundment and evapora-
tion within the impoundment for that month, or, if greater, a
volume of process wastewater equal to the difference between the
mean precipitation for that month that falls within the impound-
ment and the mean evaporation for that month as established by the
National Climatic Center, National Oceanic and Atmospheric
Administration, for the area in which such impoundment is located
(or as otherwise determined if no monthly data have been
established by the National Climatic Center)."
As delineated above, the regulatory requirements applicable to the
bauxite refining segment are essentially a qualified zero-discharge
requirement.
4. Treatment Technology
A major segment of the industry already operates its wastewater system
in essentially a zero-discharge mode. Table C-2 summarizes the steps that
must be taken (and are being taken by many plants) to achieve the qualified
zero-discharge requirement.
5. Disposal Cost
The costs of achieving the zero-discharge requirement are largely the
cost of red-mud pond construction, piping, neutralization, and any other
equipment necessary for the proper operation of a recycle system. Table C-3
summarizes disposal cost data for a number of representative plants. The
costs range from $0.27 to $0.60/short ton of alumina.
6. Wastewater Treatment Energy Consumption
Practically all of the energy required for the impoundment of red-mud•and
other waste streams is merely the electrical energy associated with pumping
the waste to the pond and returning treated water to the process.
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TABLE C-2
SUMMARY OF EFFLUENT REDUCTIONS ACHIEVED FOR BAUXITE REFINERY
PROCESS WASTES USING BEST PRACTICABLE TECHNOLOGY CURRENTLY
AVAILABLE
Ni
Waste Stream
Red Mud
Spent cleaning acid
Salt slurry from salting
out evaporator
Barometric condenser
cooling water
Barometric condenser
C.T. blowdown
"Hose-down" and cleanup
streams
Parameters
Best Practicable Control Effluent
Technology Currently Available Reduction Achievement
TDS, TSS, alkalinity Impound & recycles aqueous
phase; concentrate if
necessary
TBS , sulfates, pH
TDS, sulfates,
alkalinity
Impound in red mud lake
Impound in red mud lake
or landfill
TDS, heat, alkalinity Cool and recycle
TDS
TSS, TDS,
alkalinity
Impound in red mud lake
Recycle to process
No discharge
No discharge
No discharge
No discharge
No discharge
No discharge
Source: EPA Development Document
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I-1
TABLE C-3
SUMMARY OF WASTE DISPOSAL COST; DATA
Plant
Item
Plant Capacity,
ton/yr
Bauxite Type
Mud Ratio ^e'
Lake Capacity,
tons dry mud
AC D
Old Pond(b)
904,000 358,000 832,000
Surinam Arkansas Arkansas
0.33 2.0 2.0
4 . 63xl06 12 . 2xl06 8 . 3xl06
E(C)
New Pond(b)
832,000 1,433,000
Arkansas Jamaican
2.0 1.0
12.9xl06 59.0xl06
F B
Old Pond New Pond
617,000 617,000 1,268,000
Surinam Surinam Jamaican
0.33 0.33 1.0
3.3xl06 1.9xl06
Capital cost, $
Unit Capital cost,
$/ton mud
Annual cost, $/yr
Mud, ton/yr
Unit Annual Costs,
l.SlxlO6 1.21xl06 0.93xl06
0.318 0.1 0.11
355,000 102,000 502,000
226,000 728,000 1,675,000
2.77xl06 12.8xl06
1.69xl06 l.lOxlO6
0.22 0.22 0.635
768,000 223,000
1,279,000 206,000
0.59
Notes: (a) Mud basis, in 1975 dollars (ENR Construction Cost Index - 2126).
(b) Construction costs of old pond were expended as incurred; new pond on capitalized basis.
(c) Exemplary plant, zero discharge of pollutants.
(d) Annual costs represent average costs for two old ponds.
(e) Ib mud/lb of alumina produced.
(f) Very large lake; estimated capacity includes 20-year life still remaining.
.0.54
$/ton mud
$/ton alumina
1.57
0.53
0.14
0.27
0.29
0.58
0.60
0.60
1.09
0.36
0.43
1 ton = 2000 Ib
SOURCE: EPA Development Document
1 metric ton
106 gm
454 gm = 1 Ib
-------
Based on a red-mud generation rate of 1.5 tons of mud/ton of alumina,
and a total pumping head of 200 ft, the unit energy requirement for waste-
water treatment is 7.75 x 10~^ million Btu/ton of alumina, which is a very
small fraction of the total alumina production energy requirements.
Plants employing clarification devices for chemically treating (via
precipitation) wastewater prior to recycle will have a small additional
energy requirement.
b. Primary Aluminum Smelting
1. Present Sources of Wastewater
The potential sources of wastewater from primary aluminum smelting
include:
(a) Wet scrubbers used on potline and potroom ventilation air.
(b) Wet scrubbers used on anode bake furnace flue gas.
(c) Wet scrubbers used on casthouse gases.
Cd) Cooling water used in casting rectifiers and in fabrication.
Ce) Boiler blowdown.
These sources are very much interrelated to the type of air pollution
control systems used for particulate and fluoride control. The following
overview is taken from the EPA Development Document to describe this
interrelationship.
An Overview of the Interrelationship of Anode Type,
Process Technology, Air Pollution Control,
and Water Pollution Control*
"In the development of Effluent Limitation Guidelines for the Primary
Aluminum Industry consideration was given to the interrelationship of a
number of factors. The following discussion is concerned with the various
ways in which primary aluminum smelters have approached environmental
control. The purpose of this overview is to identify major factors.
"The specific factors that must be considered are:
Anode Type
Prebake
Horizontal Stud Soderberg
Vertical Stud Soderberg
*Source: EPA Development Document.
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Air Pollution Control Method
Hooding
Gas Cleaning
Dry Scrubbing
Wet Scrubbing
Once-through Water
Recycle Water
Anode Bake Furnace Gas (Prebake Anode Only)
Wet Scrubbing
Electrostatic Precipitators
Anode Type
"A major factor is that no Soderberg type plants have been constructed
recently, nor have any been predicted for future construction. The
principal advantage of this type of cell is the absence of a requirement for
an anode baking furnace.
The factors of electrode type most pertinent are those related to air
pollution control and include the efficiency with which cells using the
various anode types may be hooded, the nature of emissions to the air
associated with each anode type, and the air pollution control devices applic-
able to each. It is obvious that water is not used directly in any of the
types of anodes.
The major effect of differences in anode type on water usage and streams
are that for prebake anode plants, cell emissions (e.g., fluorides, SOx, COx,
etc.) are separate from anode bake plant emissions (e.g., tars and oils, etc.).
etc.). In Soderberg type operations, all of these substances are emitted
from the cell area. Current practices with regard to control (and water
usage) are discussed below.
Hooding
"The efficiency of hooding of cells is a factor which determines the air
pollution control measures required. In general, the results of current prac-
tice are that if Cgiven proper operation) hoods are sufficiently tight and
efficient, air pollution control devices may need to be applied only to
primary pot gas to meet atmospheric emissions standards. This gas may be
characterized as containing relatively high concentrations of pollutants and
is suitable for treatment by either dry or wet gas cleaning devices. If
hooding is of lower efficiency, emissions standards may necessitate the
treatment of potroom or secondary air which may be characterized as contain-
ing relatively dilute concentrations of pollutants, and the only practicable
treatment is by wet gas-cleaning devices.
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Dry Scrubbing
"Dry gas-cleaning methods involve the use of dry alumina as an adsorbent
to remove pollutants from the pot gas. The salient features of dry scrubbing
are that the adsorbent (alumina) subsequently is fed to the cells to be
reduced to aluminum metal, and that the recovery of fluoride values is vir-
tually complete. As mentioned above, dry scrubbing is applicable only to gas
streams with relatively high concentrations of pollutants, i.e., from cells
with highly efficient hoods.
The total recycle of emissions has associated with it the potential
problem of build-up of trace metals and impurities in the product.
Wet Scrubbing
"Wet gas-cleaning methods as practiced in the industry include wet
electrostatic precipitators, tower-type scrubbers, or spray type scrubbers,
alone or in combination, and with or without demisting devices. All may be
classed as low pressure-drop devices," i.e., 1-10 inches of water. No high
energy venturi type scrubbers are used in current practice. Wet scrubbing
devices may be applied to either relatively concentrated (pot) or dilute
Cpotroom) gases.
The scrubbing media are of paramount interest to this study and may be
described in terms of recirculating type systems or once-through systems.
Anode Bake Furnace Gas Scrubbers
"In prebake anode plants, the anode bake furnace gases may be controlled
by electrostatic precipitators or most commonly by wet scrubbers - again of
the "low" pressure-drop types. If wet scrubbers are used, the waste waters
contain tars, oils, SOx, COx, as well as fluorides if anode materials are
recycled from the electrolytic cells.
Applications of electrostatic precipitators are relatively limited
because of hazards stemming from arcing and subsequent burning of tars and
oils in the precipitators. Gas cooling sprays generally are applied, result-
ing in some wastewater. Such sprays are not designed to scrub fluorides,
although some incidental scrubbing action may occur, hence, the dry electro-
static precipitator is not always an adequate component to meet fluoride air
emissions regulation. Baghouses are unsuited to this purpose because of the
blinding action of the tars and oils. Thus, wet scrubbers are in some cases
the only adequate air pollution control devices for anode bake furnaces at
this time.
Current Practice
"The current practices as determined during the effluent guidelines
program are indicated by the following annotated citations of existing
examples illustrative of the combinations of the factors under discussion:
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A. (1) Plant A. Prebake Anode - totally dry scrubbing on pot gas (zero
water)
Anode Bake Plant - controlled firing
(2) Plant C. Prebake Anode - wet scrubbing on pot gas, once-through
water; dry scrubbing on some pot gas
Anode Bake Plant - wet scrubbing
(3) Plant D. Prebake Anode - wet scrubbing of secondary air; scrubber
water recycle with two-stage treatment before discharge
Anode Bake Plant - wet scrubbing with once-through water
B. (I) Plant B. Vertical Stud Soderberg - wet scrubbing of pot gas -
total recycle of scrubber water - bleed stream evaporated -
dry scrubbing planned
C. (1) Plant J. Horizontal Stud Soderberg - wet scrubbing; dry systems on
paste plant
(2) Plant F. Horizontal Stud Soderberg - wet scrubbing on pot gas
once-through water; dry scrubbing planned
"Some noteworthy factors in the above practices include further variations
of the center-break and side-break technologies within the prebake class of
plants. The center-break variation, where cell crusts are broken and
alumina charged at spots along the center of the cell is potentially the
most amenable to tight hooding and dry scrubbing. The side-break technology
is less amenable to tight hooding and thus may lead to a choice of wet scrub-
bing of secondary air. Major emphasis is placed on the fact that the anode
configuration in side-break cells allows higher electrical efficiency
C6 kWh/lb) relative to center-break cells (7-8 kWh/lb).
"The factor leading to the planned conversion of a vertical stud
Soderberg plant from wet scrubbing (but zero discharge of water) to dry
scrubbing was a need to meet a stack opacity standard which was currently
exceeded during pin changes.
"It also may be noted that one horizontal stud Soderberg plant has a
current compliance program dependent on the installation of a dry scrubbing
system."
(2) Waterborne Pollutants from Aluminum Production Employing Existing
Technology
i
The following wastewater constituents were found to be present in waste- '
water emanating from primary aluminum production:
Suspended solids,
Dissolved solids,
12-8
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Chemical oxygen demand (COD),
Oil and grease,
Fluoride,
Chloride,
Sulfate,
Free cyanide, and
Trace metals (including Zn, Cu, Ni).
The proposed effluent limitation guidelines set specific limitations only
on:
Fluoride, and
Suspended solids.
Unlike many of the industries, there is not a great deal of available
information on the raw wastewater pollutional loadings. (There is a great deal
of information in the Development Document (see Table C-4) oh the pollutional
loadings of treated effluents, but very little on the raw wastewater).
Since wastewater flow rates and the quantities of pollutants present are
so highly dependent upon the specific type of air pollution control equipment
used (wet vs dry), it is not realistic to set forth a "typical" raw wasteload
for the primary aluminum industry. The raw wasteload varies greatly from
plant to plant.
Generally, plants utilizing a once-through treatment system will have a.
unit wastewater flow rate of 4,000-40,000 gal/ton of aluminum. The fluoride
concentration in the untreated wastewater typically varies from 20-50 ppm.
The design calculations for the Development Document treatment cost estimates
assume that for a plant producing 250 ton/day of aluminum, the wastewater flow
rate will be 5 million gal/day, and will have a fluoride concentration of 35 ppm.
(3) Effluent Limitations
Three levels of effluent limitations are proposed for the primary
aluminum industry. These are listed below, along with the technology recom-
mended for their attainment:
Best Practicable Control Technology
Currently Available
The recommended effluent limitations for the primary aluminum smelting
subcategory to be achieved by July 1, 1977, and attainable through the appli-
cation of the best practicable control technology currently available are as
follows:
129
-------
Single-Day Maximum (b)
kg/kkg Al
2
3
Ib/ton Al
4
6
30-Day Average (c)
kg/kkg Al
1
1.5
Ib/ton Al
2
3
Effluent Limitations(a)
Effluent
Characteristic
Fluoride
Suspended Solids
pH Range 6-9
(a) Effluent limitations are defined as kilograms of pollutant per metric
ton of aluminum produced or pounds of pollutant per short ton of
aluminum produced.
(b) The single-day maximum is the maximum value for any one day.
(c) The 30-day average is the maximum average of daily values for any consec-
utive 30 days.
The best practicable control technology currently available for the
primary aluminum smelting subcategory is the treatment of wet scrubber water
and other fluoride-containing effluents to precipitate the fluoride, followed
By -settling of the precipitate and recycling of the clarified liquor to the
wet scrubbers as a means of controlling the volume of wastewater discharged.
Two precipitation methods are currently available: cryolite precipitation and
precipitation with lime. This technology achieves attendant reduction of the
discharge of suspended solids and oil and grease.
Alternate technologies for achieving the recommended effluent limitations
include dry fume scrubbing and total impoundment.
Best Available Technology Economically Achievable
The recommended effluent limitations to be achieved by July 1, 1983, by
application of the best available technology economically achievable are as
follows:
Effluent Limitations(a)
Effluent
Characteristic
Fluoride
Suspended Solids
pH Range 6-9
(a) Effluent limitations are defined as kilograms of pollutant per metric ton
of aluminum produced or pounds of pollutant per short ton of aluminum
produced.
(b) The single day maximum is the maximum value for any one day.
Cc) The 30-day average is the maximum average of daily values for any
consecutive 30 days.
130
Single-Day Maximum (b)
kg/kkg Al
0.1
0.2
Ib/ton Al
0.2
0.4
30-Day Average (c)
kg/kkg Al
0.05
0.1
Ib/ton Al
0.1
0.2
-------
The application of the best practicable control technology currently
available results in a relatively low-volume, high-concentration bleed stream.
The best available technology economically achievable is lime treatment of
such a bleed stream to further reduce the discharge of fluoride. This tech-
nology also achieves further reduction of the discharge of suspended solids
and oil and grease.
Alternate technologies for achieving the recommended effluent limita-
tions include dry fume scrubbing and total impoundment.
New Source Performance Standards
The recommended standards of performance for new sources attainable by
the application of the best available demonstrated control technology,
processes, operating methods, or other alternatives, are as follows:
Standards of Performance (a)
Effluent Single Day Maximum (b) 30-Day Average (c)
Characteristic kg/kkg Al Ib/ton Al kg/kkg Al Ib/ton Al
Fluoride 0.05 0.1 0.025 0.05
Suspended Solids 0.1 0.2 0.05 0.1
pH Range 6-9
(a) Standards of Performance are defined as kilograms of pollutant per metric
ton of aluminum produced or pounds of pollutant per short ton of aluminum
produced.
(b) The single day maximum is the maximum value for any one day.
(c) The 30-day average is the maximum average of daily values for any consec-
utive 30 days.
The best available demonstrated control technology, processes, operating
methods, or other alternatives consists of dry scrubbing of potline air, the
control and treatment of fluoride-containing waste streams by recycle and
treatment of any necessary bleed stream by lime precipitation, and the
treatment of casthouse cooling water and other streams, as required, for oil
and grease removal with a gravity separator or aerated lagoon.
(4) Cost of Treatment
For the types of wastewater treatment proposed in the Development
Document, most of the capital cost and a large portion of the operating cost is
directly dependent on the volumetric flow rate of wastewater treated. If this
varies over a wide range, the costs will also vary over a wide range.
The costs presented in the Development Document (and adjusted to 1975
dollars) are broken down by process alternative as shown in Table C-4.
131
-------
TABLE C-4
COSTS OF VARIOUS ALTERNATIVES FOR FLUORIDE REMOVAL
co
to
Process Alternative
Dry scrubbing
Wet scrubbing - once-through
Wet scrubbing - recycle
Recycle with bleed and
filtrate treatment
Once-through and alum
treatment
Once-through and activated
alumina treatment
Once-through and hydroxyla-
patite treatment
Once-through and reverse
osmosis treatment
Discharge
Fluoride
lb/1000 Ib
0
5
1
0.05
1
0.25
0.25
0.8
Capital Cost
$ /annual ton
48.6
9.0
12.2
14.0
22.2
11.8
26.6
_
i.uud.1.
Operating
Cost
$/ton
19.8
4.5
7.5
8.4
16.7
9.4
24.0
29.7
Electrical
(kWh/ton)
233
84
394
85-395
100
100
100
100
Thermal ,
Equivalent
(kWh/ton)
0
200
200
200
-
-
-
_
Total
233
284
594
285-595
100
100
100
100
fcft $/annual ton = total capital cost divided by annual production rate.
Includes energy requited by the scrubbing process in addition to that required for the wastewater treatment.
NOTES
1. Capital costs have been adjusted to 1975 dollars (ENR - 2126) .
2. Operating cost includes:
a. Depreciation @ 7.1% of capital investment
b. Return on investment @ 20% of capital investment
c. Admin, overhead @ 4% of operating and maintenance
d. Taxes and insurance @ 2.0% of capital
e. All energy and chemicals associated with the treatment plant.
-------
2. AIR POLLUTION
a. Emission Sources
The base line for this work is aluminum produced using the Bayer-Hall
process. Within the Bayer plant, bauxite is ground and digested to produce
sodium aluminate. The major source of emissions during this operation is the
ore grinder. After precipitation, alumina trihydrate from the Bayer plant is
calcined in a rotary kiln to produce alumina. The kiln is usually equipped
with a particulate collection device to recover the alumina dust for
economic reasons. However, the exhaust from the primary control device may
still require additional cleaning to meet standards.
At the aluminum reduction plant, alumina is reduced to aluminum in an
electrolytic cell. This operation produces particulate, sulfur, and hydro-
carbon emissions as well as fluoride emissions. The amount of emissions
depends upon the type of cell used.
(1) Prebake Cells
The electrolytic reduction of aluminum produces a CO exhaust at the anode
Of the cell. As the exhaust leaves the cell, it entrains particulates includ-
ing fluoride salts. The exhaust also contains noxious gases such as HF and
traces of H2S.
In a prebake plant the carbon anode, which is consumed as a part of the
reaction, is formed in a baking furnace. The manufacturing process is similar
to coke-making in that a paste made of pitch and coal is devolatilized forming
a solid carbon anode. The process emits large amounts of hydrocarbons, sulfur
compounds, and particulates.
C2) Soderberg Cells
Plants which use Soderberg cells do not require anode furnaces because
the anode is formed from a coke-based paste within the electrolytic cell
itself. In this case, the particulate, sulfur, and hydrocarbon emissions
common to the anode furnace of a prebake cell will be emitted in the electro-
lytic cell of the Soderberg process instead.
There are two types of Soderberg cells: horizontal stud and vertical
stud cells. With respect to air pollution control, the primary difference
Between these two is the ease with which a hood can be placed over a cell in
order to capture emissions. In horizontal stud Soderberg cells the hood does
not fit close to the pot and, therefore, large volumes of air are entrained
with the hot exhaust from the cell. This has the effect of quenching combus-
tion of hydrocarbons, thereby resulting in a large tar fouling problem as the
heavy hydrocarbons condense on ducts and control equipment.
133
-------
On the other hand, vertical stud Soderberg cells have close-fitting
hoods so that hydrocarbon combustion can occur. In this case, the hydro-
carbons are converted to C02 and a carbon dust which does not cause fouling.
b. Emission Rates
Typical rates of particulate and fluoride emissions are given in Table
C-5. Note that fluorides can be gaseous (HF) or solid (CaF2> NaF2, etc.).
The estimate of total particulates includes solid fluorides. As will be
pointed out later, not all of the particulate control devices listed in the
table are able to achieve compliance with current particulate emission stand-
ards. Plants have to rely on venturi scrubbers, electrostatic precipitators
or fabric filters. SC>2 emissions are estimated to be 60 Ib/ton of aluminum,
but of course dependent upon the sulfur content of the pitch and coke used to
manufacture the anodes (prebake cells) or anode paste (Soderberg cells).
c. Control Technology
The Bayer plant has only two sources of particulate emissions to control,
as follows:
• Particulates from the ore grinder should be collected in a hood and
removed using high-efficiency particulate removal, such as an
electrostatic precipitator, venturi scrubber, or bag filter. Low-
efficiency wet collection devices have been applied on some plants,
but are generally not effective enough to comply with current
standards.
• Particulates from the rotary kiln calcining operation are removed
using a combination of multi-cyclone and electrostatic precipitator
or bag filter. The collected dust is primarily alumina which is
recycled.
The electrolytic reduction process requires controls for particulates,
fluorides, S0£, and hydrocarbons. The control technology depends upon the
type of electrolytic cell being used. Table C-6 contains a summary of the
pertinent emission characteristics of the three cell types. Most control
systems rely primarily upon a caustic scrubber to remove particulates and
gaseous hydrofluoric acid. Note, however, the following specific problems of
each cell.
• Prebake cells - In addition to the control of the reduction cell,
controls are also required for the anode-baking furnace. Hydro-
carbon and sulfur oxides are emitted primarily in this furnace, not
in the reduction cell. Incineration or flaring will be required to
control the hydrocarbons. SC>2 will be controlled using S02 scrubbers
or low-sulfur coal and pitch.
134
-------
TABLE C-5
EMISSION FACTORS FOR PRIMARY ALUMINUM PRODUCTION PROCESSES'
a
Typeofopemlon
»•.«!» grinding"
Uncontrolled
Spiey lower
floeling-bed
Krubber
Oucneh tower end
cpreyeereen
CkctroMetic pro-
Cipiutor
dKMngoltkjmimrm
hydroilde*^
Uncontrolled
Sprev tower
Floilingbed
euubber
Quench tower and
epreyicieefl
Ekclroilitic ore-
Cipiutor
Anode beking funuce'
Uncontrolled
Sprey tower
Dry efectroiullc •
precipiuior
Self-induced eprey
ritbeked reduction
0.12
200.0
60.0
66.0
34.0
4.0
3.0
(i.otos.a*
NA
1.13
0.09
11.3
(115 tt. 177.0)
. 17J
2.02
1.62
1.82 to 8.94
16.2
16.2
12J
12.2
1X2
98.4
1 93.8 to 104.01
19.61036.4
21.6
7.10
78.4
11.6
. NA
3.14
0.784107.84
3.9704.7
1S7
10.0
'3.0_
' "2J
1.7
0.20
kc/MT
3.0
0.90
018S
0.50
0,060
100.0
10.0
28.0
17X)
3.0
u
ia5u>2.5)
NA
0.57
0.03
• 40.6S
(B.9Sto8U)
8.9S
1.01
9.31
0.61 to 4.47
8.1
8.1
6.1
6.1
0.81
49.2
(46.8 to 52.0)
9» to 18.3
IOJ
US
322
9.6
HA
I.S7
0.393 to 3.92
1J6 to 2.35
1784
,
6.0
14
1.4
0.86
0.10 •
CKeoutlluoridnlHFI
iWton
Neg
Neg
Neg
Nee
Meg
Neg
Nit
Neg
Meg
Net
033
0.0372
0.93
0.0372
24.7
(13.8 to 344)
24.7
O247
1.98105.93
34.7
0.494U) 2.72
0.494
2.96
6.4
0.494
26.6
(2S.2u>28«
1^6102.39
O.S32
36.8
30.4
(20.0 to 35 JJ)
0304
0.304
OJ04
30.4
30.4
0.608
Neg
Net
"*<
"*'
Heg
ko/Mr /
leg
Neg
Net
Neg
Neg
Neg
Neg
Neg
Ntg
Neg
0.47
0.0166
0.47
0.0186
12.35
(8.9 to 17.41
12.3S
0.124
0.99 to 2.97
12.3S
0.247 lo 1.36
0.247
1^8
43
0.247
13J
(12.« to 14.4)
0.93 1 and 3.
*He lofonutlon available.
^Controlled BKlaalon factora are baeed on averag* uneonerolled factor* and oo average
obaerved collection efflcleoclea.
'kfarencea 1, 2 and 4 through 6.
*»uaberi In parenthee» are range* of uocontrolled valuei obaerved.
''teferencei 2 and 4 through 6.
Eefaraac* 1.
^Kefarencei 2 and fi.
Sourcei Coaq>llatlon of Air follutane Caiaalon Factora,
USEPA Office of Air Trograea Fubllcatlona.
135
-------
TABLE C-6
SUMMARY OF AIR POLLUTION CHARACTERISTICS AND CONTROL
Particulates
and Gaseous
Cell Type Fluorides Fluorides Hydrocarbons Sulfur Oxides Controls
Prebake Cells Yes Yes Carbon dusr Trace Caustic scrubber
Anode Furnace Particulatss only No Volatile! Yes Hot precipitator
Incineration
S02 scrubbing
Vertical Stud Soderberg Cells Yes Yes Carbon Dust Yes Caustic scrubber
Horizontal Stud Soderberg Cells Yes Yes Tars Yes Floating bed scrubber
Present in form of SO or'H^S.
• Soderberg cells - Hydrocarbons and sulfur oxides are emitted in the
cell along with particulates and gaseous fluorides.
Vertical studs - Hooding fits close enough so that hydro-
carbons are burned, leaving only carbon dust. Controls include
caustic scrubber or wet electrostatic precipitator.
Horizontal studs - The cell exhaust is diluted with too much
excess air so that hydrocarbons do not burn out. Subsequent
condensation of tars on ducts and control equipment creates a
serious tar fouling problem. Floating bed scrubbers are often
used to .avoid fouling the control device with tar.
The above cell types are difficult to hood. Estimates have been made of the
following coverages:
TABLE C-7
PARTICULATE EMISSION CAPTURE BY CELL HOODS
Amount of Particulates Captured
Pot Type by Best Available Hooding (%)
New prebake 95
Older prebake 79
Vertical stud Soderberg 50
Horizontal stud Soderberg 80
136
-------
Because of the incomplete hooding, a large fraction of the emissions
escape collection and are emitted through roof vents or monitors in the build-
ing. In some cases, roof scrubbers have been installed to remove the gaseous
fluorides and some particulates. It is also possible to collect these
emissions in a duct along the roof line and remove the pollutants using high-
efficiency scrubbers, bag filters, or precipitators. This type of fugitive
emission control is expected to be very costly but may be required to meet
current standards.
3. SOLID WASTES
a. Process-Related Solid Wastes
The major source of solid wastes generated during aluminum production is
the red-mud engendered during the processing of bauxite to produce alumina.
This source contributes approximately 0.3 to 2 tons of solids per ton of
alumina, depending on type of raw material (as shown in Table C-3).
b. Water Pollution Control - Related Solid Wastes
Most of the water pollution control systems used in the treatment of
wastewater from primary aluminum smelting produce solid waste as an inherent
part of their operation. However, if a wet-scrubbing system is converted to a
dry-scrubbing system, it is possible to return collected particulates and
gases to the electrolytic cell.
The Development Document provides limited data on reported quantities of
solid waste, which are shown below:
Solid Waste Generation
EPA Plant Designation (Ib/ton aluminum)
C 30
D 60
G 50-60
Calcium fluoride and inert, suspended solids are the main constituents of
the solid waste.
c. Air Pollution Control-Related Solid Wastes
As noted, much of the dust generated during aluminum production from
bauxite is either alumina or fluoride salts, both of which may be returned to
the process.
These wastes amount to an insignificant fraction of the total solid wastes
from the process - primarily red-mud.
137
-------
Note, however, that the Bayer-Hall process is normally carried out in
two different locations so that the dust emissions from aluminum production
cannot be combined with the red-mud. In this case, the particulates are
either recycled or landfilled at a cost of about $5/ton. Note that proper
landfill conditions must be observed to avoid leaching fluoride salts, but
there are no other hazardous constituents in the wastes requiring more exten-
sive precautions.
138
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-76-034h
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE ENVIRONMENTAL CONSIDERATIONS OF
SELECTED ENERGY CONSERVING MANUFACTURING PROCESS OPTIONS
Vol. VIII. Alumina/Aluminum Industry Report
5. REPORT DATE
December 1976 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Arthur D. Little, Inc.
Acorn Park
Cambridge, Massachusetts 02140
10. PROGRAM ELEMENT NO.
EHE624B
11. CONTRACT/GRANT NO.
68-03-2198
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Enviornmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
FINAL
14. SPONSORING AGENCY CODE
EPA-ORD
is.SUPPLEMENTARY NOTES Vol. III-VII, EPA-600/7~76-034c through EPA-600/7-76-034g, refer t
studies of other industries as noted below; Vol. I, EPA-600/7-76-034a is the Industry
Summary Report and Vol. II, EPA-600/7-76-034b is the Industry Priority Report.
16. ABSTRACT Report.
This study assesses the likelihood of new process technology and new practices being
introduced by energy intensive industries and explores the environmental impacts of
such changes. Specifically, Vol. VIII deals with the alumina/aluminum industry. The
report examines three new process developments for producing alumina from domestic
clays as alternatives to the Bayer process: (1) nitric acid leaching process, (2) hy-
drochloric acid leaching process, (3) clay chlorination (such as the Toth alumina pro-
cess), and two process changes for the production of aluminum: (1) the Alcoa chloride
electrolysis process and (2) the application of titanium diboride cathodes to the con-
ventional Hall-Heroult cells. All of these alternatives are discussed in terms of rel
ative process economics and environmental/energy consequences. Vol. III-VII and Vol.
IX-XV deal with the following industries: iron and steel, petroleum refining, pulp
and paper, olefins, ammonia, textiles, cement, glass, chlor-alkali, phosphorus and
phosphoric acid, copper, and fertilizers. Vol. I presents the overall summation and
identification of research needs and areas of highest overall priority. Vol. II, pre-
pared early in the study, presents and describes the overview of the industries con-
sidered and presents the methodology used to select industries.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Energy
Pollution
Industrial Wastes
Alumina
Aluminum
Manufacturing Processes;
Energy Conservation;
Bayer, Hall Processes;
Toth, Clays, Alcoa
Process
13B
18. DISTRIBUTION STATEMENT
Release to public
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
155
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
139
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